The Abdication of Charles V

On 25 October 1555, the Emperor Charles V (1500–58), leaning on the shoulder of the young Prince William of Orange (1533–84), appeared at the Coudenberg Palace in Brussels before the representatives of the estates of the XVII Provinces of the Habsburg Netherlands.Footnote * He had called the assembly to witness the transfer of the rule over these lands to his son and major heir, Philip II (1527–98). It was a first step in a process whereby the old emperor divested himself of the rule over all his lands and territories. In January 1556, still at Brussels, he signed the necessary documents for the transfer of Castile and Aragon, as well as their dependencies in Italy, North Africa and the New World. Shortly after, he also abdicated the imperial title to his brother Ferdinand I (1506–64), who had ruled the Habsburg hereditary lands in and around Austria for decades and had already been elected king of Germany in 1530. This particular abdication had, however, to be held secret pending the acceptance of the transfer of the emperorship by the German electors, which would only be obtained in 1558. In the meantime, Charles appointed his son to the office of imperial vicar-general for the kingdom of Italy – that is Italy north of Rome – over which the emperor held feudal suzerainty, in order to strengthen his hold over the strategically situated Duchy of Milan and to fortify Spanish control over the smaller principalities in the region.Footnote ¹ In early 1556, the old emperor travelled to Castile, where he lived out the remainder of his life at the cloister of San Jeronimo de Yuste.Footnote ²

The emperor’s decision to abdicate was as much an acknowledgement of the failure of his European policies as it was born from the desire to make his peace with God before he died. The timing of the abdication had at first been dictated by Charles’ wish not to ratify the Peace of Augsburg of 25 September 1555 in person. This agreement, which his brother Ferdinand had negotiated with the estates of the Holy Roman Empire, conceded to Catholic as well as Lutheran princes of Germany alike the right to impose their own confession within their territories (cujus regio, ejus religio). Under pressure of his brother and son, Charles had, however, not escaped ratification and had been forced formally to underwrite in his own hand the collapse of his policies to uphold and restore the religious unity of the Empire, and by extension the whole Christian Commonwealth (respublica Christiana).Footnote ³ The process of abdication, and the negotiations about the division of the inheritance between Philip, Ferdinand and the latter’s son Maximilian II (r. 1564–76), also put an end to Charles’ hopes to pass on the imperial title to his son after Ferdinand’s death, and thus keep a link between the most important lands of the Habsburg Monarchy, the Spanish kingdoms and the elective emperorship. With this, any aspirations to ‘universal monarchy’ over Latin Christianity that Spanish kings might entertain were severely jeopardised in advance. Once Ferdinand was effectively raised to the imperial dignity in 1558, Philip II of Spain had to release his pretences to the position of imperial vicar-general or deputy for Italy.Footnote ⁴

The context and manner of Charles’ relinquishment of the reins of power were a far cry from the hopes and acclamation with which his ascendancy as the foremost prince of Europe, about thirty-five years earlier, had been met. As a young man, Charles of Habsburg had fallen heir to an extraordinary set of lands, territories and titles, making him the most powerful ruler within the Christian Commonwealth since Charlemagne (r. 768–814). To the Netherlands, which he inherited from his father Philip the Fair (r. 1482–1506) in 1506, came the rule over the kingdoms of Castile and Aragon, at the death of his maternal grandfather Ferdinand the Catholic (r. 1479–1516) ten years later. The kingdoms of the Baleares, Sardinia, Sicily and Naples were attached in personal union to the Crown of Aragon, as were the title to the defunct crusader Kingdom of Jerusalem, Ferdinand’s claims to the likewise bygone Byzantine empire of Constantinople, his conquests on the coasts of North Africa and his hopes and dreams to launch an eastwards crusade and reconquer both Jerusalem and Constantinople.Footnote ⁵ The death of Charles’ paternal grandfather, Emperor Maximilian I (r. 1493–1519) opened the door to his election as Roman-German king and delivered the imperial title into his hands in 1519. The rule of Maximilian’s Austrian lands was left to his brother Ferdinand, who would later add the kingdom of Bohemia and what remained of the kingdom of Hungary after the death of their previous king at the battle of Mohacs (1526) against the troops of the Ottoman Sultan Suleiman the Magnificent (r. 1520–66). In the year 1519, the Spanish conquest of Mexico against the Aztec and Maya began. In the early 1530s, other expeditions would lead to the destruction and subjection of the Quecha empire of the Inca in the central Andes.Footnote ⁶

Charles’ rise to prominence among the Christian rulers was hailed by some as the work of divine providence at a time of peril for the Christian Commonwealth. His accumulation of lands and power, and his acquisition of the imperial title were seen as an assignment by God to unite Christianity in the face of the Ottoman threat. The offence launched by Sultan Selim I (r. 1512–20) against the Persians and the Mamluks had led to the conquest of Syria, Mesopotamia and Egypt by 1517 and had left the Ottomans as the dominant land and maritime power in the eastern Mediterranean, ready to strike at Italy and the western Mediterranean. The fall of Belgrade (1521), Rhodes (the basis of the order of Saint John, 1522) and Hungary (1526) brought the Habsburg lands in Austria into the line of fire, with the siege of Vienna (1529) as dramatic proof of the vulnerability of the very heartlands of the West. To the threat of the Ottomans, soon the affliction of religious division, of heresy in the eyes of the Catholic Habsburgs and their supporters, was added with the rise of first Lutheranism and then other Protestant confessions.Footnote ⁷ At a time when the old order of the Christian Commonwealth had to face the double threat of internal and external destruction, God seemed to have provided an instrument of reform, restoration and reconquest through the young Emperor Charles V.

The Ottoman threat led to the revival of old late medieval ideas about the unity of the Latin West and the necessity of internal peace to launch a counteroffensive against the Ottomans. For this, one natural strategy was to look for a guiding role to the traditional heads of the Christian Commonwealth, its spiritual head, the pope, and its secular head, the emperor. In answer to the Ottoman advances in the east, Pope Leo X (r. 1513–21) had twice promulgated a five-year truce among all Christian princes and called for the crusade. In 1518, the initiative had been wrested from his hands by Cardinal Thomas Wolsey (1473–1530), chancellor of England, who brokered a permanent and ‘universal’ peace treaty among the leading powers of Europe.Footnote ⁸ The election of Charles V in June 1519 seemed to some to give Christian Europe a natural, secular leader. For the first time in centuries, the imperial crown was resting on the head of a man who, thanks to his rule of Spain, parts of Italy and the Netherlands, had the power and resources to fulfil the old universalist aspiration of the emperorship.

None was more vocal or prominent in the government of Charles V among the spokesmen for the resurrection of the old idea of the emperor as the ‘universal monarch’ of the Latin West than Mercurino di Gattinara (1465–1530). Gattinara was a civil lawyer from Northern Italy who had previously served Charles’ aunt and governor-general of the Netherlands, Margaret of Austria (1480–1530). In 1516, he had penned an oration about universal monarchy, which he dedicated to the young Charles. In late 1518, Gattinara was raised to the office of grand chancellor of Charles for all his lands, and put at the head of the small central bureaucracy that had to aid Charles in overseeing and ruling his vast collection of lands.

For the occasion of the reception of the German delegation to Spain that came to affirm Charles’ election in late 1519, Gattinara composed an oration in which he stated that Charles’ elevation was a sign that he was God’s instrument to reform and restore Christianity and overcome its enemies. For this, the chancellor drew on both medieval eschatological ideas about the coming of a last empire that would bring peace and prepare for the second coming of Christ, as well as on the secular Roman law tradition of the emperor as ‘lord of the world’ (dominus mundi). The latter tradition had found a powerful articulation in De monarchia by the poet Dante Alighieri (1265–1321) and had been worked out in its legal intricacies by Italian commentators of civil law of the fourteenth century, foremost among them Bartolus of Saxoferrato (c. 1313/14–57) and Baldus de Ubaldis (1327–1400), as part of their discussions on public authority, jurisdiction and empire.Footnote ⁹

Late medieval civil as well as canon lawyers had struggled with aligning the idea of the emperor as universal monarch with the reality of the Holy Roman Empire’s geographical limitation to the kingdoms of Germany and Italy. By the fourteenth century, the independence of the rulers of the realms outside of the Empire as ‘superiorem non-recognoscentes’ (those who do not recognise any superior) was commonly accepted. The notion of the independence of the kings of France, and others, had found powerful support through the decree of Pope Innocent III (r. 1198–1216) Per venerabilem (1202). In the fourteenth century, it was widely acknowledged that the kings of the realms outside the Empire held similar, supreme jurisdiction, or powers of lawmaking and law enforcement, as the emperor (‘rex imperator in regno suo’; the king is emperor in his own realm). The solution to bridge the gap between the reality of several independent kingdoms and the claim about the emperor as ‘lord of the world’Footnote ¹⁰ was to distinguish the de facto independence of Christian rulers from the de jure universal authority of the emperor. This solution was embraced and given powerful authority by the leading commentators of civil law, Bartolus and Baldus. Bartolus stated that those who rejected the universal authority of the emperor de jure were heretics, thus equating ‘universal empire’ with the community of Christians. Under the de facto/de jure distinction, factual independence amounted to more than usurpation and was considered legitimate if it was acquired through legally valid means such as consent or prescription. The princes of the realms outside Germany and Italy thus enjoyed full and supreme jurisdiction over their domains – at least in secular matters – without interference from the emperor. The polities and princes of the kingdom of Italy held far-reaching autonomy and wide jurisdiction, albeit within the framework of the feudal overlordship of the emperor as suzerain, when available. The emperor, as de jure ‘lord of the world’, retained, however, sole secular jurisdiction over the Christian world as a whole. This assigned certain tasks and powers to him. He was the primary defender of Christianity against its external enemies, held responsibility for protecting the faith and correcting the Church hierarchy when necessary, and was the heir to the Roman emperors as promulgator and guarantor of Roman law.Footnote ¹¹ The distinction fitted the Aristotelian–Thomistic theory that each entity, including polities, drew legitimacy from its own ends, but at the same time participated in the higher ends of the entities it was part of, and ultimately of the Christian community, which was to approach God. The emperor stood as the secular head of a multi-layered hierarchy wherein many members enjoyed original and supreme jurisdiction, but wherein he held responsibility and power over some aspects of the governance of the whole. As ‘lord of the world’, he held jurisdiction over the whole, but no superior jurisdiction over its composing parts.Footnote ¹²

In their writings and actions, Gattinara and his supporters rehearsed these ideas and moulded them into policies to serve their agenda both for the internal governance of Charles’ empire and for its foreign relations. On the internal level, the discourse of universal empire suited Gattinara to strengthen his position as grand chancellor over the different bureaucracies in the composing parts of the empire. The idea of Charles as the divinely appointed vindicator of the unity of Christianity allowed Gattinara to detach the emperorship from its historic moorings in Germany and thus counter the potential opposition by the German-imperial chancery to his centralising policies. It allowed him to cater to the sensitivities of the Castilian elite. Thus, Gattinara contributed to later ideas about the transfer of the seat of empire to Castile, which gained force after the abdication of Charles.Footnote ¹³ With regards to external policy, Gattinara applied the language of universal empire both to the outer-European world and, most significantly, to the Christian Commonwealth. As Gattinara indicated in his oration of 1519, the election of Charles to the imperial dignity gave him a right to conquer the whole, non-Christian world. Thus, he endorsed Spanish expansion in the New World. With regard to the Christian Commonwealth, he employed the idea of universal monarchy in the Bartolist sense. For Gattinara, this had three major practical implications: the creation of a lasting peace among Christian princes under the guidance of the emperor, the hegemony over Italy as the basis for this peace and as a stepping stone towards leading a crusade against the Ottomans and the reform and restoration of the Church, through the convocation of a general Church Council.Footnote ¹⁴

Charles V himself never fully embraced the universalist programme of Gattinara and his faction at court. For him, the concerns about the preservation of his inheritance and dynastic rights came first. However, he also took his role as defender of the faith and Christianity against its internal and external enemies to heart and, when the opportunity arose, did not stop Gattinara from pressing claims to a special role for the emperor in the governance of the Christian Commonwealth. The high watermark for Charles’ claim to universal monarchy came after the victory of his armies at the Battle of Pavia (1525), where his nemesis, the French King Francis I (r. 1515–47) was taken captive. The discussions for what became the Peace Treaty of Madrid (1526), led to a clash between the emperor and his chancellor, and the latter’s refusal to attach his chancellor’s seal to the treaty. Whereas Charles chose to make peace with Francis in order to pursue his dynastic claims to full sovereignty over his French fiefs in the Netherlands as well as to the duchies of Burgundy and Milan, Gattinara preferred a more stable alliance with the Italian principalities against France under the emperor’s benign hegemony. The repudiation by Francis of his commitment to restore Burgundy upon his release and the ensuing formation of the anti-imperial League of Cognac with the French king and the pope restored the unity between Charles and his grand chancellor. After imperial troops had captured and sacked Rome (1527), the anti-Habsburg coalition broke and the imperial government could roll out a successful policy towards Spanish hegemony in Italy, attain a renewed peace with France (Peace of Cambrai, 1529) and ensure the coronation of Charles by the pope (1530).Footnote ¹⁵

Charles V’s government made the most blatant affirmations of universal monarchy in the treaties of Madrid with Francis I and of Barcelona with the pope (1529). Article 23 of the Peace of Madrid imposed an obligation on Francis I to aid a military expedition of Charles to Italy with troops, ships and money. Under Article 25, both princes committed to ask the pope to call a general council that would work for universal peace and deal with both the ‘Turks’ and heretics, as well as to request the pope to grant them the most extensive privileges – including privileges on church taxes – for a crusade for three years. In case the crusade could not be launched in time and an Ottoman attack against Christianity or Italy occurred, Charles would, as ‘head of the secular princes of Christianity, to whom the defence thereof falls in first order’, assume the defence with the aid of France, the knights of Saint John and Genoa. All troops would be put under the command of an imperial general.Footnote ¹⁶ The Barcelona Treaty, which Gattinara had negotiated himself, called the emperor ‘protector and defender of the Holy Roman Church and the Apostolic See, and head of the Christian Commonwealth’.Footnote ¹⁷ At the Peace of Cambrai, the imperialist faction already had to climb down from the lofty heights of these universalist claims. The emperor was no longer named as ‘head of the secular princes of Christianity’ and the article on joining a crusade under the leadership of the emperor was barred. The article on French aid for an Italian expedition by Charles was less open-ended now (Article 29), and went along with the undertaking by France not to interfere in the affairs of the Empire and Italy (Article 27). With the Peace of Cambrai, France had to relinquish its dynastic claims to territories in Italy (mainly Milan and Naples) and accept the factual hegemony of Charles over the peninsula, but without any references to the discourse of universal monarchy.Footnote ¹⁸

After the coronation of Charles V at Bologna and the death of Gattinara, both in 1530, the discourse and policies of universal monarchy receded into the background. The final decade of Charles’ reign, however, was marked by a revived focus on his role as defender and restorer of the faith, with regards to both crusading and Protestantism.Footnote ¹⁹ However, the discourse of universal monarchy was operated less, or in more subdued manners. Under the Peace of Crépy with Francis I (1544), which opened the way for Charles to confront the growing power of the Protestants in Germany, Charles and Francis promised to engage, jointly albeit not equally, in a crusade. Francis committed himself one-sidedly to send a given number of troops for the planned expedition against the Ottomans to Hungary.Footnote ²⁰ A day after the treaty was signed, the French king promised the same aid for an offensive against the Protestants to Charles or his brother, the Roman king, in Germany. If this implied a recognition of the rights of the emperor in the defence of the Christian – i.e. Catholic – faith, it was a localised one. Francis also promised his support for the convocation of a general council, which would finally meet at Trent the year after. Contrary to what some historians have stated, this promise was not part of an additional secret treaty but took the form of a unilateral declaration by Francis I.Footnote ²¹ This implied that non-performance to these commitments would not violate the treaty and end the peace. After Madrid, Crépy marked a highpoint in Charles’ pursuance of an agenda as defender of Christianity, as well as of his factual ascendancy over his major contender, but the discourse of universal monarchy remained largely unemployed. The preservation of dynastic right and the fight for the defence of Habsburg lands against the Ottomans in Hungary and the Mediterranean, as well as the Habsburg-Catholic position in the Empire were now paramount. In the following year, Charles would lead his troops first to victory (at the Battle of Mühlberg, 1547) against the Schmalkaldic League of German Protestants, and then defeat against a Franco-Protestant alliance (1552), and saw his hopes for returning the emperorship to the Spanish branch of the Habsburgs dashed. After the abdication of Charles V, all references to a universalist role of the emperor or the Spanish king remained defunct. The Peace Treaty of Le Cateau-Cambrésis (1559) between Philip II and Henry II of France (r. 1547–59) mentioned the joint support of both kings to the Church council, but at a level of strict equality.Footnote ²²

With the scission of the emperorship from the Crown of Castile, any dreams of restoring the unity of Christianity, whether in the religious or in the political sense, and of achieving a lasting peace under the leadership of a universal monarch receded. The Spanish Monarchy, now the predominant power in Europe, had to redirect its imperial ambitions within Christian Europe to a doctrine of divinely granted duty of protection of the Catholic Church against both its internal Christian and Muslim enemies, but could only sustain these in a localised manner. The focus was on the defence of the existing territories of the Spanish Monarchy. Outside Europe, imperialist ideas, which were drawn from the medieval traditions of civil and canon law, were refashioned to debate and justify claims to an exclusive right for the Iberian powers – which between 1580 and 1640 were united under the Spanish kings – to navigate the world seas, as well as to trade and conquer in non-Christian lands.Footnote ²³

The Late Medieval Christian Commonwealth (c. 1000–1492)

The reign of Charles V can be read, with just a touch of dramatic exaggeration, as the final convulsion of the old universalist order of the Christian Commonwealth under the dual leadership of pope and emperor. The hopes that some had attached to the imperial election of Charles V ended in utter failure and speeded his abdication from power together with his surrender of the last vestiges of any ambition to universal monarchy in the late medieval sense. Henceforth, the discourse of universal monarchy became a weapon of choice for the opponents of the leading Catholic power, first Spain and from the 1660s onwards France, to accuse it of seeking the domination over Europe and the destruction of the liberty and sovereignty of other powers.Footnote ²⁴

The most essential feature of the late medieval political and legal order of the Christian Commonwealth was its dualistic nature. The secular order was the sphere of relations among human beings in the short space of life on earth. The spiritual order pertained to the relation between God and human beings. Both had their own laws and their own jurisdiction: the external forum that controlled and sanctioned human actions towards one another, and the internal forum, or the forum of conscience, where the eternal fate of each individual soul would be decided after death, and at God’s final judgement at the end of times.

The secular order of late medieval Europe was marked by a far-reaching dispersion and fragmentation of public authority and jurisdiction. It was a multilayered order, wherein a great number and variety of polities co-existed, cooperated and competed. These, often overlapping, layers stretched from the Holy Roman Empire and the great and middle kingdoms such as those of France, Castile, Aragon, Naples, Hungary, Portugal, England, Scotland, Denmark, Sweden or Poland over all kinds and sizes of principalities, cities, church territories in the middle to seignories, rural communities and corporations at the bottom. While many of these only held public power and jurisdiction through delegation from above in the context of feudal vassalage, public appointment or the division of dominium (lordship, used to refer to both jurisdiction and possession), many held original jurisdiction in their own name, at least for certain areas of governance. This meant that some polities and their courts could hold supreme jurisdiction in certain matters, while being under the control or appellate jurisdiction in others. Each polity also had its own laws (jura propria) with its own legal institutions or courts. The complexity of these territorial divisions was further enhanced, within one and the same polity, because different laws, privileges and immunities applied to different classes, or estates, such as nobles, clergy, burghers, commoners, tenants and serfs, but also to particular categories of people such as students, widows, orphans, Jews and generally foreigners. These estates and classes would at times also fall under the personal jurisdiction of their own courts. This was the application of the principle of judicium parium, or judgement by peers.

Although the distinction between private and public law was known from Roman law and held increasing relevance in discussions on law and governance,Footnote ²⁵ there was no functional separation between a private and a public order. Elements of jurisdiction were often subject to private titles and thus, in modern terms, belonged to a person’s private patrimony. Under the feudal and seignorial systems, as well as through increasingly complex methods of finance, landownership was often divided between holders of title (dominium directum) and actual possessors (dominium utile), or chains of these bilateral divisions. Much of this would endure until the end of the Old Regime.Footnote ²⁶

The territorial and personal, or vertical and horizontal fragmentation of power, laws and jurisdiction also meant that many polities, at different levels of the pyramid of power division, engaged directly in matters of war, peace, diplomacy, treaty making and the regulation of international trade. These forms of external relations were not considered the preserve of a single layer of rulers at the top of the pyramid. By consequence, there was no need or space for a strictly separate legal category or body of rules to regulate interstate relations, nor to separate public inter-polity from private trans-polity relations.

For all these fragmentations and divisions, elites also thought of the Christian Commonwealth as a political and legal community. Real divisions were mitigated and to some extent countered by ideas and institutions of unity, that derived from the common faith and adherence to the Roman Church, as well as from the intellectual and idealistic inheritance of the Roman Empire. The resurrection of the imperial title, first under Charlemagne and then within the construction of the Holy Roman Empire, and the re-exploration of Roman imperial law through the learned, university study of the codification by the Emperor Justinian (r. 527–65) had led to the promulgation and the promotion of the idea of the emperor as lord of the world and as universal monarch over Christianity under the dynasty of the Hohenstaufen (1138–1254). The demise of the dynasty ended any real chance at vesting a form of concrete jurisdiction outside the actual borders of the Holy Roman Empire, but the ideal of the emperor as a monarch for the whole of the Christian Commonwealth was worked out by the civilians of the late thirteenth and fourteenth centuries and lingered on. Moreover, the model of the Roman emperor’s lawmaking political thinkers made their conceptions of royal power.Footnote ²⁷

If universal monarchy for the emperor proved an unattainable ideal, Roman or civil law formed a more robust pillar under the idea of unity within the secular sphere. Since the rediscovery of the Digest in Italy in the late eleventh century, and the spread of universities within and outside of Italy from then onwards, Roman law together with canon law had become the object of a continuous learned exploration and study that reached the outer fringes of Christian Europe to the west (Ireland), east (Poland and the Baltic) and north (Sweden) by the early sixteenth century at the latest. Roman law was only applicable law, and then mostly as subsidiary law, in the southern parts of Christian Europe. However, under the scholastic epistemology and methodology, which dominated at late medieval universities in all disciplines, the codification by Justinian was granted an almost absolute authority, second only to the Bible, in the fields of secular law and governance. Scholars studied, interpreted and plundered the Digest and the other parts of the collation by Justinian in the expectation of extracting an absolute, complete and consistent truth about questions of justice and governance from it. As such, Roman law was seen as an embodiment of perfection, inasmuch as revealed by God and inasmuch as humans could ever hope to attain it through reason. It was an authoritative fountain of wisdom and justice for lawyers and governors to take inspiration from in the interpretation or improvement of their local laws. In those parts of Europe where Roman law had no formal standing as applicable ‘written law’ (lex scripta), it was considered ‘written reason’ (ratio scripta) and served as a treasure trove to search and find a just answer to about any question of secular law and governance. It also served as a major source of inspiration for canon lawyers, and was, surely from the late thirteenth century onwards, often considered in conjunction with canon law in order to address theoretical or current practical issues. Roman and canon law thus formed part of a common learned discourse in Christian Europe, the jus commune. The medieval collation of Roman law also came to include the Libri feudorum, a codification of feudal customary law made by Lombard lawyers in the late twelfth century. This made feudal law into an object of study and discussion at universities.Footnote ²⁸

The spiritual sphere concerned the eternal life and the chance of salvation of each Christian soul. Under mainstream late medieval dogma, the fate of each individual Christian was determined by the sum of her sins or good deeds during life. With the emergence of the sacrament of confession, the spiritual fate was not only individualised under the dogma of free will but also became highly juridical. In the confessional, the governance of the human conscience – the internal forum – and her relation with God as the final judge came into the hands of Church-appointed, ordained priests who weighed the remorse of a person and granted absolution for eternal punishment pending the performance of penance. For this, theologians and canon lawyers produced the so-called books of penance (libri poenitentiales) that listed sins and their appropriate penance. The first function of canon law was thus similar to that of modern criminal law: the definition of sins and the indication of an earthly punishment, in this case in order to gain absolution from eternal punishment.Footnote ²⁹

Since the Gregorian Reform under Pope Gregory VII (r. 1073–85) and the emergence of the papal monarchy in the twelfth and thirteenth centuries all over the Western Church, the governance and jurisdiction over the spiritual sphere had become highly centralised. Through a hierarchy of metropolitan and other archbishops, bishops and parish priests, a hierarchical network of ecclesiastical courts and the controlling and guiding role of papal legates, the papacy had its power felt all though Christian Europe and its dependencies, such as the crusader principalities in the Middle East. Canon law formed a primary language and instrument of government, the dispensation of justice and papal control. As the papacy successfully established the independence of the Church from secular authority and wrested control of the so-called jus in sacris (jurisdiction over the external governance of the Church and its property and the regulation of rituals)Footnote ³⁰ from the hands of the emperor through the Investiture Controversy and other secular rulers, the body of canon law dealing with these matters grew dramatically.Footnote ³¹

Between the Gregorian Reform and the crises of the papacy that came with the ‘Babylonian exile’ in Avignon (1307–77) and the Great Schism (1378–1415), the body of canon law expanded into an equally sophisticated and impressive pillar of the common legal order of Europe as Roman law, the so-called classical canon law (1140–1314). The great collections, starting with the Decretum Gratiani (c. 1140) that was given papal sanction through the first official codification, the Liber extra (1234), became subject to university study at the faculties of canon law, in parallel with the collection by Justinian at the faculties of civil law. If the canon law texts shared from the same intellectual authority as the Roman law texts under the scholastic paradigm, they also contained a law that was applicable throughout Christian Europe, in the Europe-wide network of ecclesiastical courts that operated under the supreme control of the papacy and its courts.Footnote ³²

Moreover, the ambit of canon law and the jurisdiction of the ecclesiastical courts were not restricted to the internal forum or the management of Church and faith. Between the late twelfth and the middle of the thirteenth century, it became well established that the Church, and thus the papacy, held at least indirect jurisdiction over secular affairs inasmuch as this was necessary to render justice in the internal forum. As it was a general principle of canon law that sins could not be forgiven if the sinner had not restored the damage done to another person first, the jurisdiction of the ecclesiastical courts potentially extended to all matters relating to sin (ratione peccati). Canon law thus addressed many issues of secular, inter-human relations. The decree Novit Ille of Innocent III would confirm this while at the same time restricting the claims of the Church to more serious sins.Footnote ³³ With the scholarly writings and papacy of Sinibaldo Fieschi, or Pope Innocent IV (r. 1243–54), the principle of indirect jurisdiction (or implied powers) in the secular sphere would also become applied to the question of the proselytisation of the faith and relations with non-Christian peoples. It formed a central plank in the argumentation of canon lawyers and theologians about the justification of imperial expansion outside Europe, during and after the Middle Ages.Footnote ³⁴

Neither Roman law or canon law dealt systematically with the regulation of inter-polity or trans-polity relations as a separate body of issues, let alone law. The codification of Justinian contained relatively few direct references to Roman inter-polity law.Footnote ³⁵ But both sets of texts were considered as authoritative, complete and consistent sources to what constituted just human behaviour, in the spiritual and/or secular spheres. This meant that the whole tradition of authoritative Roman as well as canon law texts, their doctrines, institutions, rules and arguments, could be brought to bear on matters of war, peace, treaty making, diplomacy, territorial acquisition or trade. In this manner, norms and institutions that had originally applied to private relations among individuals were directly applied to relations between polities and rulers. Roman and canon law, often in conjunction through their joint study and consideration in commentaries and learned advises (consilia) by jurists who had a background in both laws (utriusque juris), thus formed a major source for the formation of doctrines and practices in the sphere of inter- and trans-polity relations. This was not a matter of application by analogy, as ‘international law’ was not considered a separate body of law, but part and parcel of a general discourse on law, justice and governance that extended to all types of relations within the Christian Commonwealth, or in relation to God. Canon law, even more than Roman law, stood at the foundation of this common, Europe-wide legal order, as ecclesiastical courts, and the papacy itself, could and did claim jurisdiction, or frequently offered their arbitration in matters of war, peace and general diplomacy.Footnote ³⁶ The custom to ratify treaties by oath made their violation a mortal sin (perjury) that squarely fell with the ambit of Church courts.Footnote ³⁷ As dynastic marriages formed a major instrument of diplomacy and cause for territorial claims, and marriage was a sacrament, disputes arising therefrom also were a frequent issue of consideration for the ecclesiastical courts and the papacy.Footnote ³⁸

The Crisis of the Christian Commonwealth

The diplomatic and military events that wrecked any chance for a resurrection of universal monarchy under Charles V were only the outer appearances of more structural changes that disrupted the late medieval order of the Christian Commonwealth and brought it down by the middle of the sixteenth century. What followed, was a long period of crisis and transition. The century after the abdication of Charles V was marred by violent religious and civil conflicts within the major countries of Christian Europe, great power wars among the Christian powers and against the Ottoman Empire, increasing imperial and commercial competition between Europeans outside Europe, and the lack of consent about the political and legal order of Europe. The crisis culminated in the great conflagrations of the Thirty Years War in and over the Holy Roman Empire (1618–48), the Franco-Spanish War (1635–59) and a series of civil revolts and wars that plagued many of the leading countries of Europe in the middle of the seventeenth century. It was only after 1660, when most of these conflicts had been settled, that consent about a more stable, albeit endemically violent order could be reached within Christin Europe: that of the society of sovereign rulers and their states.Footnote ³⁹

There were three structural disruptions that led to the demise of the old universalist ideals of the Christian Commonwealth and caused a deep and transformative crisis in Christian Europe. Firstly, there was the collapse of Christian unity under the papal Church of Rome. Within the span of a generation after Martin Luther (1483–1546) first mounted his challenge to the papacy by nailing his ninety-five theological theses on the door of the church in Wittenberg (1517), Western Christendom fell apart into a Catholic south and a Protestant north. By 1550, Sweden and Denmark-Norway, as well as many of the German estates, had embraced Lutheranism, while in England the Anglican Church had been established by Henry VIII (r. 1509–47) and his successor Edward VI (r. 1547–53), and then again, after a brief return to Catholicism under Mary I (r. 1553–8), Elisabeth I (r. 1558–1603). In the decades before and after 1550, Calvinism would rapidly gain traction in the Habsburg Netherlands and France, especially among nobles and the urban elites. In the Netherlands, resistance against the repression of Protestantism by the Habsburg government mixed with discontent about royal centralisation policies and led to open revolt, armed repression and finally the secession of the northern provinces and the formation of the Republic of the United Provinces of the Netherlands (Eighty Years War, 1567–1648).Footnote ⁴⁰ France went through a series of religious wars between Catholics and Huguenots (1562–98 and 1627–9), wherein the French Crown itself became the object of contention after the Huguenot leader, Henri of Bourbon-Navarre, the future Henri IV (r. 1589–1610) became heir presumptive in 1584.Footnote ⁴¹ The Catholic counteroffensive, known as the Counter-Reformation, was launched with the Council of Trent (1545–63) and largely eradicated Protestantism from the south of Europe, while helping to secure Catholic victories in France, southern Germany, Hungary and Poland. Although religious divisions would continue to play a significant role in national and international conflicts and alliance building throughout the Old Regime era, the Thirty Years War in the Empire, which started over Bohemia, may be considered, among others, the last of the great religious wars among the Christian confessions in Europe.Footnote ⁴²

The loss of religious unity and the confessional strife tumbled the major pillar under the legal order of the Christian Commonwealth. By the middle of the sixteenth century, a large part of Europe rejected the papacy, its Europe-wide jurisdiction, unitary court system and lawmaking power. With this, the ultimate authority under many legal doctrines and practices that regulated inter- and trans-polity relations collapsed and European legal scholars as well as governors and diplomats found themselves without a common legal ground to organise relations between the different Christian confessions. Within a short span of time, canon law and ecclesiastical jurisdiction also lost their attraction for the regulation of inter-polity and trans-polity relations among Catholics. The dependency of the Church on Catholic princes to defend itself, and the example of Protestant princes, inspired Catholic rulers to roll back papal claims to jurisdiction in secular matters and to strengthen control over the external government of the Church in their own domains.

The procedure of treaty making illustrates the sudden collapse of canon law and ecclesiastical jurisdiction as a pillar under the legal order of Europe well. Since the Middle Ages, it had been customary for princes and rulers to ratify treaties by oath. This was commonly done in church and was accompanied by rituals such as touching the Gospels and relics from saints. This gave added strength to the binding force of the treaty under canon law and brought its upholding and interpretation clearly under the jurisdiction of the Church courts. In important treaties of the late fifteenth or early sixteenth centuries, the signatory parties often expressly invoked the pope’s jurisdiction and submitted themselves to canonical sanctions. Although the practice of confirmation by oath continued until the late seventeenth century, express references to canonical jurisdiction or sanctions disappeared by the second half of the sixteenth century, first from treaties involving Protestants and then from treaties among Catholics.Footnote ⁴³ The collapse of canon law as the common basis under the legal order of Europe forced scholars and practitioners of international governance to find another basis of common authority to reconstruct the legal order of Christian Europe, one that transcended the divides between the different confessions. Scholars, ranging from the earlier neo-scholastics to Hugo Grotius (1583–1645), would ultimately find the answer by reconceptualising natural law and the law of nations into more secular, more autonomous and more dense legal categories than they had been under late medieval law.

Secondly, the Renaissance period saw the gradual emergence of some great dynastic monarchies, and a few republics, which were increasingly successful in monopolising warfare and external policy land and in excluding smaller or dependent players. In this, a series of transformations in military technology and warfare, known in historiography as the ‘Military Revolution’, played a central role. Ever since Michael Roberts launched his thesis that a ‘Military Revolution’ took place between 1560 and 1660, historians have debated the merits of this thesis.Footnote ⁴⁴ Historians have argued about the exact periodisation, the relative role of certain technologies, tactical innovation or political processes, the interaction between military innovation and state building and its impact on European empire building. There is, however, consent about some broad tenets of the Military Revolution thesis. It is generally accepted that the gradual introduction of gunpower, first in the decades before and after 1500 with artillery on land and ships, then in the decades before and after 1600 with individual firearms, was part of a transformation that led to the expansion of armies and of warfare itself and the drastic rise of the cost of armies, navies and war. The expansion of war implied that only a limited number of powers could henceforth mobilise sufficient manpower and financial means effectively to wage and sustain war. This forced governments to strengthen the bureaucratic and legal means for the extraction of resources and to enhance their demographic and tax basis, while at the same time allowing them to crowd out smaller powers within and beyond the borders of their lands.Footnote ⁴⁵ While historians have debated the relative role of military innovation and state building in terms of cause and effect, the more sound approach seems considering them as connected parts of a transformation that saw the expansion of war and the expansion of state governments and bureaucracies go hand in hand and feed off one another. War became the core business of states, and only of states. Whereas war and the diplomacy around it had been the business of numerous sovereign and non-sovereign agents during the late Middle Ages, by the end of the Renaissance period it had largely become – with the exception of the Holy Roman Empire – the preserve of a single layer of polities, the sovereign monarchies, realms and republics of Europe. Smaller power brokers were eliminated as autonomous agents from the field of war- and peacemaking. This meant that they were altogether excluded from the business of war, or incorporated in the armed forces and diplomatic services of greater sovereign rulers, either as public officers or mercenary entrepreneurs.Footnote ⁴⁶

Thirdly, the discoveries and imperial expansion in Africa, Asia and America were also disruptive to the old order of Europe. On the one hand, from the very first decades of the exploration of and beyond the Atlantic Ocean, they caused new, and often violent, competition between European powers and their representatives. Although private entrepreneurs of all kinds – navigators, merchants, missionaries – played a key role in the expeditions, they mostly did so under an official sanction by sovereign rulers. Governments thus held stakes of reputation and material gain. As wars among European rulers became increasingly endemic and encompassing, competition for new natural resources and new markets outside Europe gradually gained significance as a factor of European policy. Although it took until the eighteenth century for inner- and outer-European war and diplomacy to become integrated and aligned in terms of grand strategy, military tactics and legal processes of war- and peacemaking,Footnote ⁴⁷ the ambition to monopolise non-European waters and lands and exclude other European powers from them was a practical and legal concern for governments from the very beginning. The claim to a monopoly over navigation, trade and government outside Europe of the Iberian powers on the basis of papal grants was contested and rejected by other European powers, but the principle of monopolies by European powers over effectively held lands was commonly accepted.Footnote ⁴⁸

Historians of international law have since long considered the ‘discoveries’, commonly dated from Christopher Columbus’ (1451–1506) first transatlantic voyage in 1492, as a major factor in the turn from the medieval to the early modern legal order of Europe.Footnote ⁴⁹ The significance of the discoveries and imperialism in the prevailing narratives of the history of international law has moreover been much enhanced by the early twentieth-century debate about the ‘founders’ or ‘fathers’ of modern international law. The major thrust behind the promotion by both the US international lawyer James Brown Scott (1866–1943) and his major European ally Camilo Barcia Trelles (1888–1977) of Francisco de Vitoria (c. 1483–1546) as the founder of modern international law over Hugo Grotius, was to place the discovery and European colonisation of the American continent at the centre of the historical narrative of the origins of modern international law.Footnote ⁵⁰

The discovery of the New World, with hitherto unknown lands and peoples, gave a new impetus to debates about international order and governance. It was forced to re-explore old questions relating to the relations, peaceful and violent, with non-Christian peoples that had previously been debated in the context of crusading, but for a very different reality. This was disruptive to the mental framework of the old Christian Commonwealth. It challenged the equation between Christianity and the world order, and struck another blow at the universality of the existing legal order that was based on canon and Roman law. It necessitated the reconceptualisation of the world order on the basis of authority that transcended not only canon law, as the Reformation had done, but also Roman law. Here too, the answer was found by displacing the old jus commune as the basis of legal order with natural law and the law of nations.

A Europe of Composite and Transactional States

The disruptions caused by the loss of confessional unity, the emergence of the state as a war machine and the discoveries caused the effective and mental collapse of the old universalist framework of the Christian Commonwealth and set Western Christianity on a path of turmoil and a deep structural transformation that would last from the middle of the sixteenth to the middle of the seventeenth century. Gradually, the paradigm of sovereignty came to the fore as the leading organising principle of inner-European order, although it would take until the early eighteenth century before a new consent about an order of sovereign rulers and states would be in place.

The concept of sovereignty had been debated in the civilian, canon law and theological literature of the late Middle Ages. The major concerns that animated these debates were the relation between secular and spiritual powers, the external (in)dependence of kings and princes in respect of the emperor and the extent of a supreme power’s domestic jurisdiction.Footnote ⁵¹ Renaissance thinkers of sovereignty, such as Jean Bodin (1530–1596) heavily drew on the medieval literature and traditions but focused more, if not exclusively – as the external independence of the kings and princes of Europe had largely been achieved by the mid-sixteenth century – on the question of the internal jurisdiction of the rulers within their realm, both in secular matters and in relation to faith and church.Footnote ⁵²

Bodin famously defined (internal) sovereignty as absolute, eternal and indivisible. In his major treatise on political theory, Six Books on the Commonwealth (1576), he insisted on the supreme lawmaking authority of sovereign rulers within their realm.Footnote ⁵³ The prince was not just the guardian and guarantor of the law, but also its maker. As such, sovereigns were not bound by their own laws – under the old Roman law adagium ‘princeps legibus solutus’ –Footnote ⁵⁴ but only to higher laws such as divine law, natural law, the law of nations and the fundamental, constitutional norms of the realm that underpinned their own authority. In this sense, the power of the sovereign was absolute. ‘Indivisible’ implied that the major powers of state, which Bodin listed, originally derived from the sovereign. These powers could be delegated, but were exercised in the name of the sovereign and could never by definitely alienated.Footnote ⁵⁵

Among these key powers of state a prince had to control was the power of ‘declaring and terminating war’.Footnote ⁵⁶ From the late sixteenth century onwards, the concept of sovereignty would quickly emerge as the paradigm, which the kings and ruling bodies of the great realms and republics would operate to enhance their level of control and attain a monopoly over the core aspects of the external affairs of their polities, including war, treaty making, diplomacy and the regulation and taxation of important trade streams. This presupposed a measure of control over internal aspects of governance such as taxation, military recruitment, local government, the judiciary and lawmaking itself. With the collapse of the universalist authorities of papacy and empire in the first half of the sixteenth century, the great realms and republics of Christian Europe quite suddenly achieved their external independence in secular affairs by about 1550. But the establishment of internal sovereignty over the major aspects of public authority, including the management of its external policies, would be a much more gradual and protracted affair. Attempts by central governments to enhance their governmental, jurisdictional and fiscal control over their polities and elites led to resistance, revolt and rebellion, which was in some senses exacerbated by internal religious contention and international interventions and war. The 1640s and 1650s were particularly violent in this respect, with the ongoing war over Germany (1618–48) and major rebellions and civil wars in France with the Fronde (1647–53), Spain with the Catalan (1640–53) and Portuguese (1640–68) attempts at secession, and the British Isles with the civil wars (1639–53) and the period of the Commonwealth (1649–60). The ending and outcomes of these conflicts, whether secessions failed as in the case of Catalonia or succeeded as in the case of Portugal and the Dutch Republic, led in most cases to more stable regimes and enhanced control of central governments from the 1660s onwards.Footnote ⁵⁷ By the second half of the seventeenth century, in most of the important countries of Europe, central governments had achieved a measure of control over the central aspects of governance, including their external affairs, that allow us to consider them as the sovereign power brokers of their polity. This did not mean or necessitate that subaltern powers were completely eliminated from agency at the international level. It did mean, however, that the paradigm of sovereignty henceforth prevailed as the organising principle of international governance. A single layer of polities, that of the supreme realms and republics, had broken free from the amalgam of the multilayered order of late medieval Europe and had defined a plane of international relations, and law, which became their exclusive preserve. Germany, and to a lesser extent Northern Italy, formed an exception. The Peace Treaties of Münster and Osnabrück of 24 October 1648 that ended the Thirty Years War laid down a new constitutional settlement for the Holy Roman Empire that sustained a division of power, also in relation to external affairs, between the imperial institutions and the over 300 estates – princes, cities and ecclesiastical territories – of the Empire. Under the two Westphalia peace treaties, these estates saw their right to an autonomous external policy confirmed. The peace treaties subscribed to their right to make treaties among one another, or with foreign powers, as long as they were not directed against the Empire or emperor, or against the internal peace of the Empire.Footnote ⁵⁸

The idea of the gradual formation of a society of sovereign powers of ‘states’ during the Renaissance on the ruins of the Christian commonwealth comes with three qualifications. Firstly, most sovereign rulers governed over so-called composite monarchies. The most powerful, sovereign powers in Renaissance Europe were not unitary, centralised units of governments, but compositions of several, formerly separate units. The composing units might be contingent, as in the case of the lands of the Austrian Habsburgs or the personal union between England and Scotland, or might lay widely apart as in the case of the Dutch and Italian possessions of the Spanish Monarchy. Imperial expansion outside Europe added to this organisational complexity. The composite monarchies were mostly forged through the historic accumulation of rights over different territories by the reigning dynasty through conquest, treaties, inheritance, marriage, donation, enfeoffment or purchase. They were thus held together in personal union by a common prince, whereby the extent of control by a central, princely bureaucracy greatly varied. Also in historic kingdoms, whose core territories had belonged to the realm for centuries like in the case of France, there existed great differences among different provinces of the realm with regard to the balance between jurisdictional control and autonomy of the centre and local elites. In most cases, central governments had to leave large measures of autonomy and had to respect local laws and privileges, a reality with which the desire for sovereignty stood in constant dynamic tension. This reality, however, made sovereignty over the core aspects of external policy all the more significant to the monarchy. As war was the core business of the monarchy, control over war, and the diplomacy and trade policies that were connected to it, needed to be its preserve for it to survive. The same was true for ‘composite republics’ as the Dutch Republic of the United Provinces or the Swiss Confederacy.Footnote ⁵⁹

Secondly, the gradual monopolisation of external governance by the sovereign was as much a matter of including and incorporating hitherto autonomous elite players – territorial rulers of dependent principalities, military nobility, ecclesiastical princes and city governors – into the governmental machinery of state than of their exclusion. With regard to external relations as much as internal governance, central governments co-opted these elites through transactional devices whereby they outsourced certain aspects of sovereign power. The enlisting of mercenary captains (condotierri), privateering and the granting of concessions or monopolies to merchant corporations for navigation, trade and colonisation outside Europe are among the most cited examples thereof.Footnote ⁶⁰ These were quite a natural and common feature of what may be coined the ‘transactional state’ of the Renaissance and later that, in stark defiance of a modern understanding of sovereignty, did not impose a strict separation between public power and private patrimony. In fact, in the short run, the imposition of sovereignty over hitherto autonomous players such as feudal princes and powerful cities often amounted to little more than transforming the form of their participation in external affairs by redefining an old autonomous right into a right based on contractual delegation. Outsourcing governmental power remained also a major instrument of interior management, as tax farming, the granting of economic concessions and monopolies and the perseverance of seignorial justice in many countries of Europe illustrate. Moreover, the borderlines between outsourcing and incorporation within the public sphere were thin. The replacement of mercenary captains by appointed officers, or displacement of local lords by royal governors was often relative because of the existence of patrimonial rights over offices and the formation of dynasties of army and naval officers, bureaucrats and diplomats. In a sense, the monarchies were dynastic from top to bottom, with the logic of dynastic rights and their preservation determining not only the composition of the monarchy but also its internal governmental structure.Footnote ⁶¹ Finally, the vague distinctions between private and public or between central government and local elites meant that, outside the paradigmatic preservation of the ‘international’ domain and its law to a single layer of sovereign powers, ‘transnational’ relations between nobles, princes, clerics, co-religionists and all kinds of corporations and institutions continued, whether or not under the aegis of a transactional delegation from the sovereign. Forms of diplomacy or treaty making among non-sovereign actors were largely ostracised from the literature of the law of nations, while the terminology of diplomacy, war or treaties was made exclusive to relations among sovereigns. This, however, did not stop these transnational relations and networks to persist, whether or not under the formal cloak of inter-sovereign diplomacy.Footnote ⁶²

The practice of treaty making illustrates this. From the fourteenth century onwards, important treaties were sometimes co-ratified by prominent subjects and cities of the signatory parties. These co-ratifications served as a guarantee for the upholding of the treaty as these persons and entities promised to come to the aid of the victim of a violation of the treaty. But they also bound the co-ratifying subjects directly to the treaty, making them players on the international field in their own right.Footnote ⁶³ By the middle of the sixteenth century, the practice had fallen into disuse. Instead, between the mid-fifteenth and mid-sixteenth century, a shift occurred towards more institutional and less personal forms of internal guarantees, such as the practice from Franco-Habsburg peace treaties whereby it was stipulated that the parties would have the treaty registered by their supreme courts, chambers of accountancy or representative assemblies. These registrations did not bind individual subjects or cities to the treaty but ensured that their clauses would be applied by these courts and institutions as part of the law of the land.Footnote ⁶⁴ Another example of the formal submission of subjects under the cloak of sovereignty is the practice of providing concrete stipulations with regards to private claims and rights of important subjects in peace treaties, or additional ‘treaties on particulars’, rather than having these subjects deal directly with the foreign power.Footnote ⁶⁵

Thirdly, European rulers still considered themselves part of a community of Christian powers, whose confessional unity was deplorably but not irretrievably lost. Treaties, also between powers that belonged to different confessions, still referred to peace within Christianity as a common goal. Until the end of the sixteenth century, preambles invoked the restoration or maintenance of peace among Christians as a necessary precondition to fight the external enemies of Christianity, the ‘Turks’. In reality, however, Christian powers like France made common cause with the Ottomans against the Habsburgs, their common enemy, or established long-term diplomatic relations with them. References to the idea of ‘Christian’ or universal peace were reiterated through the Renaissance and Old Regime periods.Footnote ⁶⁶ Until and beyond the end of the Renaissance, treaties were made under the invocation of the name of God and the Holy Trinity.Footnote ⁶⁷ As, increasingly, great power confrontations, such as the wars between France and the Habsburgs, turned into multilateral coalition diplomacy and warfare, Christian Europe grew into a veritable system or society of sovereign rulers with common institutions and procedures of diplomacy, dispute settlement, trade and security management. Permanent diplomatic missions and multilateral peace conferences, such as Westphalia (1643–8), became part of the governance system of Christian Europe by the end of the Renaissance.Footnote ⁶⁸

Whereas the law of nations was designed as a system to manage disputes and conflicts over rights and pretences among sovereign powers, the same sovereigns also acknowledged that they shared responsibility for the common good of the Christian community because they were the supreme, secular rulers within that community. This common discourse, however, served rather as a platform to claim moral superiority over competitors and as a weapon in the fight for or against dominion over Christian Europe than it served as the intellectual foundation for common peace. The brief episode of ‘universal peace’ under the Treaty of London of 1518 illustrates this well.Footnote ⁶⁹

The Emergence of the Law of Nations as a Scholarly Discipline

For over two hundred years, international lawyers have indicated the Renaissance period as the beginnings of the ‘science’ of international law. In his 1785 survey of law of nations literature, Dietrich Heinrich Ludwig von Ompteda (1746–1803) singled out the first publication of Hugo Grotius’ De jure belli ac pacis libri tres in 1625 as the starting point of the modern period (‘neuere Zeit’) in the historical development of the law of nations.Footnote ⁷⁰ Grotius’ position as founder of the modern discipline of the law of nations remained unassailable until some scholars in the late nineteenth century, chief among them Ernest Nys (1851–1920) began to delve into the late medieval and Renaissance literature from before Grotius.Footnote ⁷¹ It was, however, the offensive by James Brown Scott and his allies to promote the role of Vitoria and other leading members of the School of Salamanca that was most successful in extending the purview of international law’s intellectual history to the early sixteenth century. Scott’s edition of The Classics of International Law has gone a long way towards establishing the place of Vitoria and Francisco Suárez (1548–1617), but also of the jurists Pierino Belli (1502–75), Balthasar de Ayala (1548–84) and Alberico Gentili (1552–1608) among the earliest representatives of the scholarship of the law of nations.Footnote ⁷² These debates about the ‘founders of international law’, which exercised scholars until late into the twentieth century, cast the contribution to the development of modern international law doctrine of late medieval scholars into a dark shadow. Until very recently, only a few scholars have delved into the theories and doctrines of late medieval scholars, and especially civilians and canon lawyers, with relation to the legal regulation of international governance.Footnote ⁷³

The Renaissance was undeniably marked by a remarkable growth in scholarly interest and an intensification of debates about the legal regulation of international relations. This came in answer to the turmoil and disruption of the old order of the Christian Commonwealth and the new challenges this brought. The period saw the emergence of the law of nations as an autonomous discipline, with its own literature, epistemologies and systematisations. This process of emancipation did, however, not constitute a radical break with the relevant late medieval intellectual traditions of – in that order of importance – canon law, Roman law and theology. Many of the doctrines and institutions on international law and governance that late medieval scholars had articulated and applied to concrete cases, often with great sophistication, were adopted. They were adapted to the new framework of the emerging society of sovereign rulers or to new questions such as the discoveries and conquests in the New World. They were recycled and transplanted from their old vessels of canon and Roman law that had lost their common authority into the newly elaborated vessels of natural law and the law of nations, which offered a new foundation of common authority.Footnote ⁷⁴

Late medieval scholars did not treat the legal regulation of international relations and governance as a self-standing object of study, necessitating a separate body of laws. Although the conceptions of natural law and the law of nations as ‘universal’ laws were known and debated, discussion was generally restricted to theoretical musings about their general nature. These categories were not filled out into elaborate masses of rules, doctrines and institutions. References were restricted to questions about the origins and nature of some universal institutions such as slavery, war or property, which had been listed under the definitions by the Roman jurist Hermogenian or Saint Isidore of Seville (560–636).Footnote ⁷⁵ Questions of war, peace, treaty making, territory, dynastic marriages, feudality, trade and navigation or dispute settlements between polities and rules were, however, lavishly discussed as common questions of civil and canon law, without necessarily classing these under the law of nature or of nations. Systematic, self-standing treatises on such matters began to appear only in the fourteenth century and remained rare and far between. The commentaries and debates by late medieval canonists and civilians on questions of international relations and governance were dispersed through their glosses and commentaries on the authoritative texts of their discipline, the collection by Justinian or Decretum Gratiani and later papal codifications, at places where a sedes materiae could be found that allowed to link an issue of international relations to the text. As jurists easily and naturally applied doctrines of private law to matters of a public nature and vice versa, this was not restricted to those few passages in the Digest or Codex that dealt with Roman international relations. In addition, many learned opinions (consilia) that jurists produced in great mass to advise on current questions or court cases also contained elaborate doctrinal expositions on international issues.Footnote ⁷⁶

The disruptions of the late medieval order and the crisis of the international system of Christian Europe not only forced Renaissance jurists and theologians to revisit old theories and doctrines and adapted them to changing political and economic circumstances, but also chased them from the disciplinary frameworks and epistemologies of canon and Roman law. Canon law lost its place as the ultimate common foundation of the legal order of Christian Europe and both branches of the jus commune were acknowledged not to offer an appropriate basis for relations with non-Christian peoples. The rejection of the universal authority of the pope and the emperor in secular matters by Vitoria and later neo-scholastics offers a good illustration of this insight.Footnote ⁷⁷ By consequence, scholars needed to indicate a new common basis for legal authority that transcended the confessional divides within Christianity and the religious and cultural differences without. Natural law and the law of nations served that dual purpose.

Modern historians of international law have generally subdivided Renaissance writers on the law of nations into two groups. On the one hand, there is the so-called School of Salamanca, whose engagement with international relations is said to have started with the lectures on the Indies by the Dominican theologian Francisco de Vitoria at Salamanca in the late 1530s and culminates in the major treatise De legibus as Deo legislatore (1612) from the Jesuit professor of theology at Coimbra, Francisco Suárez. On the other hand, there are the systematic expositions on war, peace or diplomacy in treatises written by civilian jurists, which began to appear from the second half of the sixteenth century onwards. Grotius may be said to have offered a grand synthesis of these two traditions in his De jure belli ac pacis. Its fame and success during the Old Regime period cast its forebears into quasi-oblivion until modern historians of international law rediscovered them.Footnote ⁷⁸

Over the past decades, students of the international thought and law of the Renaissance have often thought of these historic writers in terms of the opposition of (neo-)scholastic theologians versus humanist lawyers and political theorists. Whereas most consider this as a methodological division, some have underscored that these schools held opposing political views about international order, whereby the neo-scholastics adhered to more communitarian views and the humanists more blatantly endorsed the liberty and sovereignty of states to pursue their self-preservation and security.Footnote ⁷⁹ Although such oppositions have merit, one should be careful not to overstate their importance and approach them with nuance. Neither the ‘neo-scholastic theologians’ nor the ‘humanist jurists’ formed monolithic schools of thought. The methodological similarities within either of the two traditions offered a common space and epistemology for debate rather than platforms on which to construe opposite systems of international order. Moreover, these two approaches did not operate in isolation from one another but mutually influenced each other’s methodologies and doctrinal positions. The most significant distinction between the two was probably that they belonged to different intellectual traditions with different purposes. For the neo-scholastics these were theology and canon law, and the governance of the spiritual sphere; for the civil lawyers these were civil and canon law, and the governance of the secular sphere.

As professors of theology, the major representatives of the School of Salamanca, ranging from Vitoria to Suárez, were primarily concerned with the education and training of priests for their future roles as confessors and spiritual guides to kings and commoners alike. Like their late medieval forebears, these moral theologians discussed the governance of conscience in juridical terms. In the context of the Catholic counteroffensive against Protestantism, they underscored the key role of the sacrament of confession, the mediating role of priests and the Church hierarchy between humans and God, and the direct relation between the behaviour of humans on earth and their eternal fate. The neo-scholastic explorations of legal theory and doctrine were part and parcel of their rejection of the very foundations of Lutheran thought. Luther’s view that the natural world and human nature were irredeemable, that human actions did not determine one’s eternal fate and that only God’s grace could bring salvation implied a rejection of the mediating role of the Church hierarchy in the governance of conscience and separated adherence to human-made law from salvation. Even if other Lutheran and Protestant theologians would mitigate this final point, and stress the role of human-made law as an instrument of divinely appointed rulers to alleviate chaos in the sinful world and consider obedience to it as a sign of divine grace, the extension of the purview of moral theology to the whole field of laws – secular as well as spiritual – was an essential part of the Catholic Counter-Reformation.Footnote ⁸⁰

In the tradition of Thomistic legal theory, the neo-scholastic moral theologians considered all law, natural law as well as human-made laws, regardless of their constitutive or epistemological source, as geared towards the ulterior purpose of divine will, and their transgression as sinful. The emergence of probabilism, whereby the sinful character of a human action had to be decided through weighing different possible actions in terms of what was morally probable rather than certain, added thick layers of legal sophistication and drove these theologians further towards complex casuistry.Footnote ⁸¹

In 1509, the Flemish theologian Pieter Cnockaert (c. 1450–1514), with whom Vitoria studied at Paris, exchanged the Sententiae of Peter Lombard (1095–1160) for the Summa theologiae of Saint Thomas Aquinas (c. 1225–74) as the major object of his lectures and commentaries. The publication of the commentaries of Thomas de Vio, Cardinal Cajetanus (1469–1534), gave a further push to the revival of Thomism in the study of theology. Francisco de Vitoria was only one among several, and not the earliest, to bring this renewed interest in Aquinas to Spain and use Aquinas’ major treatise as the basis for a more systematic and rationally organised discussion about legal theory and law. His lectures on the Summa theologiae, as well as his public lectures (relectiones) on topical questions, such as those on the conquests in the Indies,Footnote ⁸² were published after his death through the endeavours of his student Domingo de Soto (1494–1560), himself a professor of theology at Salamanca and a councillor and confessor to Charles V. Soto expanded the by then traditional commentaries on the title ‘De justitia et jure’ from the Summa into a self-standing, systematic treatise (1553).Footnote ⁸³ It was through his and later writers’ treatises De justitia et jure, that the neo-scholastics contributed most to general legal theory as well as the systematisation of legal doctrine in different branches of the law, whether it concerned religion, private law, crime or public governance.Footnote ⁸⁴ The genre culminated in Suárez’ opus magnum from 1612, De legibus ac Deo legislatore.Footnote ⁸⁵

For their part, the civilian jurisprudents of the law of nations were concerned with the secular sphere and the external forum. Major civilian writers on the law of nations, such as Ayala, Fernando Vázquez de Menchaca (1512–69) or Gentili as well as the polymath Grotius, were deeply influenced by humanism.Footnote ⁸⁶ They extended the purview of their textual sources beyond the collection of Justinian to include newly discovered historical, philosophical, oratorical and literary texts from Roman and Greek Antiquity and shared in the critical attitude towards the medieval authors. They did not, however, break loose from the medieval traditions of civil law or canon law and continued to use the writings of the scholastic lawyers of the jus commune. As Alain Wijffels has recently argued, medieval jurists formed the major category of jurists to whom Grotius referred in his treatise on the laws of war- and peacemaking.Footnote ⁸⁷

Modern scholars have sometimes been led astray by the virulent attack by humanists of the fifteenth century such as Lorenzo Valla (1407–57) on medieval lawyers, or by the many critical comments on the latter’s concrete propositions made by humanist jurisprudents of the sixteenth century such as Guillaume Budé (1467–1540) or Jacques Cujas (1522–90). This has given rise to the myth that the humanist authors of the law of nations jumped over the medieval tradition of the jus commune and directly engaged with Roman law texts without the latter’s mediation. None of the jurisprudents of the law of nations from the Renaissance, however, ignored this tradition. They looked at it through a new, critical lens.Footnote ⁸⁸ Rather than making a stark opposition between scholastic approaches to Roman and canon law and a new humanist approach to classical Antiquity, including Roman law, the development of legal scholarship throughout the Renaissance period was marked by the gradual confluence of scholastic and humanist approaches into a new form of jurisprudence, which historians have labelled the usus modernus Pandectarum of the later seventeenth and eighteenth centuries.Footnote ⁸⁹

Humanism had its impact felt on the study of law in three major ways. Firstly, it shifted the paradigm under which the collection of Justinian, henceforth known as the Corpus juris civilis, was studied. Whereas the late medieval scholastics had granted it absolute authority as the embodiment of divinely revealed law and justice, humanists considered it a human achievement, contingent upon time and space. The Corpus juris civilis was not studied any longer because it contained a universal and timeless truth, but because it bore testimony to the highest human achievement in law and justice. For a correct understanding of the authentic meaning of Roman law, these texts were to be related to the historical contexts from which they emerged, whether political, social, economic, religious, intellectual or linguistic. Whereas historical studies had been the primary focus of humanist jurisprudents such as Cujas, later jurists who were influenced by humanism, including Ayala, Gentili or Grotius, were rather concerned with the intellectual construction of the law for current purposes. The paradigmatic change from an absolute to a relative authority of Roman law did not preclude these jurists from harvesting the Roman law texts. Roman law served as role model – as did ancient history, philosophy, oratory or literature –, as a source of knowledge about the most developed and sophisticated civilisation, and its law, from human history. The Corpus juris civilis, and other legal as well as historical texts that informed about Roman law, abounded with examples of human actions and ideas that could be emulated in order to construe an ideal law for the present. For this, endurable principles and doctrines had to be abstracted from their original contexts and adapted to present-day needs and circumstances. Humanism in the long run thus caused a shift in focus from interpreting the text of the Corpus juris civilis to using it as a treasure trove for information to construe a new law and new theory of justice. In view of its relative authority as an exemplum, Roman law needed to be critically assessed in terms of its accordance with natural justice and the dictates of human reason, and confronted with a wide array of other textual sources, which likewise informed on human achievements in law and justice.

Secondly, the understanding of the historical contingency of Roman law spurred a growing sensitivity to the regional and temporal varieties of law. This destroyed the absolute authority of Roman law as a common basis for universal law and justice and fostered interest in local legal systems and their textual testimonies. As the Renaissance period progressed, humanism became a powerful tool for lawyers to advance the agendas of national governments and aid in the construction of a national legal tradition. Some jurists insisted that Roman law was nothing but the civil law – that is, the municipal law – of the Romans themselves and had to give way to local customs and laws (jura propria) in the articulation of their own national jurisprudence. Humanism thus merged with the desire for a national jurisprudence into what became known as historical jurisprudence. In the case of some Protestant scholars, an aversion to Roman law flowing from its connotations to the papacy was added to the mix.Footnote ⁹⁰ For other jurists, Protestants as well as Catholics, Roman law retained a privileged position in their intellectual constructions of jurisprudence. To them, Roman law was the closest, or at least most likely the closest approximation of natural justice humankind had ever achieved. This rested on the presumption that Roman law, which was not only the municipal law of the greatest and longest empire ever but had also been widely acknowledged in later times, had to be in accordance with natural justice. A wide consent thus became the basis for inductively recognising natural justice. Roman law was a treasure trove of information about law, from which general principles of justice could be abstracted, then to be adapted to the concrete circumstances of time, place or discipline of their current use and implementation. In this respect, humanism was a key factor in the fragmentation of the study of Roman law into national traditions in the context of the usus modernus Pandectarum. At the same time, it forced scholars to establish a new basis of authority under the international order and aided the emancipation of the law of nations as a separate and self-standing category of law. To Gentili, Grotius and many of the modern natural lawyers of the seventeenth and eighteenth centuries, Roman law remained an important source of inspiration about the principles of justice.Footnote ⁹¹

Thirdly, as the neo-scholastics had done for theology, humanist jurists contributed towards a novel, more rational and logical systematisation of Roman law and jurisprudence. They displaced the traditional so-called ordo legalis of the subdivisions of the Digest into books, titles and leges (laws), which was far from logical, with the more systematic one of the Institutes of Justinian. This was a short and systematic introductory textbook to Roman law that was based on the once popular Institutes of Gaius, the text of which would only be rediscovered in the early nineteenth century. The division of private law into persons, property and obligations (including contracts and delicts) that Hugo Donellus (1527–91) introduced on the basis of the Institutes would not only become standard for private law in many countries of the civil law tradition but was also used by Grotius as the basis for his theory of just causes for war, and the backbone for his ventures into natural law throughout the second book of his De jure belli ac pacis.Footnote ⁹² The renewed focus on rational systematisation became, by the later sixteenth century, a hallmark of humanist education, including in law and theology – the latter in particular through the Jesuit order to which many of the later neo-scholastics belonged. It translated into a preference for treatises over commentaries as the major form of scholarly expression.

Humanism greatly contributed to the emergence of an autonomous jurisprudence of the law of nations, which culminated in the treatises on the laws of war- and peacemaking by Gentili and Grotius.Footnote ⁹³ The shift to the humanist epistemological paradigm paved the way towards the novel, logical systematisation of these core issues of the law of nations. It allowed for an eclectic use of historic, textual sources ranging from classical Antiquity and early Christianity over the Middle Ages to contemporary texts in order to explore human history and ideas. This eclectic approach, combined with rational systematisation, offered a platform to construe by induction a system of international justice that was meant to approximate the dictates of natural, and ultimately divine reason, while adapting these principles to the changed circumstances of their own times and the demands of their new discipline. This allowed them to redesign old doctrines, such as those of the acquisition of property,Footnote ⁹⁴ just war,Footnote ⁹⁵ reprisalFootnote ⁹⁶ or diplomatic representationFootnote ⁹⁷ to the needs of the emerging sovereign states and their imperial and commercial agendas. The sensitivity towards the historical contingency of all human law allowed for the law to be undone from the more concrete aspects of its historical manifestation in order that it work flexibly with the general, timeless principles of which this manifestation bore witness. Under this methodology, the gains from a historically contingent study of human laws, ideas and actions could be brought to bear on abstract, rational deductions from first insights into divine will and creation. Grotius’ re-systematisation of natural law, and the law of nations, first in his De jure praedae commentarius (written 1604–6) and then in his mature De jure belli ac pacis (1625), would fully exploit the benefits of the humanist methodology, while he drew on some of the main insights into abstract legal theory of some leading neo-scholastics. He himself acknowledged in De jure belli ac pacis that the search for natural justice could be done both through deductive reasoning from first principles of natural law, and through inductive explorations of human history and law in search for those ideas and practices that were shared by all, or at least by the more ‘civilised’ (moratiores) peoples.Footnote ⁹⁸

The Law of Nations as a Distinct Body of Law

In 1650, Richard Zouche (1589–1650), a former student of Gentili and one of his successors to the Regius Chair of Civil Law at Oxford, published a treatise on the legal regulation of relations between sovereign states in times of war and peace. Following Gentili, he restricted the subject to its secular dimension; following Grotius he defined the law of nations as a separate, positive body of law that was the preserve of sovereigns:

Zouche used the term jus inter gentes (law between nations) or jus feciale, herewith referring to the body of customs and rituals of the college of priests who were responsible for Rom’s relations with its neighbours in archaic times.Footnote ¹⁰¹ For Zouche, this law was human-made and was based on consent, which was expressed in either treaties or customs. His definition made a distinction, which would become a hallmark of later definitions of the classical law of nations or modern international law, between particular law that only applied between certain nations, and general law, that applied to all nations within ‘the community’ of nations. The latter could be based on either common consent, or the commonality of ideas. Such commonality could only be explained on the basis of concordance with the first principles of nature, which tied it back to natural reason and natural law. Zouche’s brief, introductory foray into legal theory opened the door to an eclectic perusal of sources about historic human laws, ideas and actions.

Zouche’s treatise indicates that, by the end of the Renaissance, the idea of interstate law as the subject of a separate body of positive law and of an autonomous jurisprudential discipline was gaining traction. For this, the term law of nations (jus gentium) would remain the dominant choice, until it was superseded by Jeremy Bentham’s (1748–1832) ‘international law’ in the twentieth century.Footnote ¹⁰² This did not mean that the term law of nations would henceforth be used exclusively in the sole meaning of positive, public inter-state law, nor that it cut its moorings from natural law. It had, however, grown into a legal paradigm that supported the claim of sovereign princes and rulers to an exclusive jurisdiction over key aspects of international governance, such as warfare, treaty making, diplomacy, the fiscal regulation of trade or empire-building. It was a weapon both to exclude other, subaltern power brokers and to include them through contractual transactions and monopolies. The law of nations was the exclusive, shared arena for sovereign polities to cooperate, compete and manage their mutual conflicts. By establishing it, the sovereign polities, while being one’s main competitors and often enemies, aided one another in pressing their claims to an exclusive external jurisdiction against all other sorts of public authorities.

The emancipation of the law of nations into a separate category of ‘positive, public international law’ was the result of the endeavours of both neo-scholastic theologians and humanist jurisprudents of the Renaissance. Their theoretical reflections on the place of the law of nations among the different categories of law, however, drew heavily on late medieval scholarship.

Mainstream late medieval legal theory – whether by theologians, canonists or civilians – distinguished between four major categories of laws. Referring to the definitions by Saint Isidore, Gratian gave the division between divine law, natural law, the law of nations and civil law an authoritative basis for later legal and theological scholars to debate.Footnote ¹⁰³ The law of nations differed from civil law through the range of its application: while the latter was proper to a particular nation, the former was understood as a law that was common to ‘almost’ all nations.Footnote ¹⁰⁴ Under this understanding, the Roman civil law (jus civile) was the particular law of the Roman people.Footnote ¹⁰⁵

The relation between natural law and the law of nations was a major point of theoretical discussion among late medieval scholars, as it would be among their early modern successors. The question of their interrelation stood at the heart of the question of the precise understanding of the nature, origins and field of application of the law of nations. Peter Haggenmacher, in his monumental study on the late medieval and Renaissance sources of Grotius, has indicated two major traditions.Footnote ¹⁰⁶ On the one hand, there is what one could call a rationalist tradition, of which Thomas Aquinas was the foremost representative. Although this tradition would remain at the heart of theological theories about law and be revived and refashioned through the works of the neo-scholastic theologians of the Renaissance, it also drew on legal sources and was shared among both canonists and civilians.Footnote ¹⁰⁷ Under the legal theory of Aquinas, all laws from natural law over the law of nations to human-made civil laws, stood in a hierarchical relation to the ultimate source of justice, divine law. Although they had different sources and purposes, they were also supposed to be judged, from the perspective of a person’s spiritual well-being, in terms of their approximation of the ulterior goal of understanding and approaching God and of reaching celestial beatitude in the eternal afterlife. Natural law was the human participation in divine law through reasonable insight in creation. Natural law, as an expression of divine reason, applied to all rational human beings in common. It was hence immutable. The law of nations was also common to all human beings but was not immutable. It consisted of institutions and rules that gave a more concrete articulation to the precepts of natural law. The latter law consisted of a few very general principles of justice, which were largely left undetermined with regards to the conditions of their concrete application in the secular sphere. The law of nations gave concrete substance to these principles and adapted them to the changing circumstances of the human condition. Aquinas classified the law of nations as positive law. This did not imply, however, that its source was human free will or consent. Human agency was restricted to a rational process of deduction and adaptation from natural law. As a law common to all humankind, the law of nations, like natural law, applied to relations between polities as well as relations between subjects from different polities, or referred to the commonalities between different civil laws, such as the common existence of institutions like contracts or property, and other institutions likewise mentioned by Hermogenian.Footnote ¹⁰⁸ Other late medieval writers explained the derivations from natural law under the law of nations by exploiting the canonists’ division of the rules of natural law into commands and prohibitions on the one hand, and into exhortations and permissions on the other hand. The law of nations was seen as the law that filled out this latter space of permissive natural law with concrete regulations for human behaviour. For instance, the law of nature neither commanded nor forbade the establishment of individual property; the law of nations introduced and sanctioned it.Footnote ¹⁰⁹

The second tradition rooted in the different definitions of natural law and law of nations from the Digest’s title ‘De justitia et jure’. On this textual basis, the commentators reclassified the law of nature and of nations into three categories through the introduction of two distinctions. Building on Ulpian’s (d. 228) definition of natural law as the law common to all creatures, and of the law of nations as the law common to all humans, a distinction was made between jus naturale primaevum and a jus naturale secundarium. The first was the instinctive law inherent to all living beings; the second the law of reasonable principles common to all humankind. This aligned Ulpian’s definition of jus gentium with that of Gaius, as the commentators equated this secondary law of nature with the jus gentium primaevum. From this primary law of nations, a secondary law of nations was distinguished. This latter law was also common to all humanity but differed from the secondary law of nature/primary law of nations as it emerged through human agency. For this, late medieval scholars could refer to the definition of Hermogenian of the law of nations, or of Saint Isidore as included in Gratian, which listed a number of human institutions, many of which pertained to the relations between polities such as war, treaties or diplomacy, as instances of law of nations.Footnote ¹¹⁰ To explain the potential derogation of this secondary, positive law of nations from the divinely created principles of natural law, theologians and canonists could draw on the postlapsarian traditions that originated in Saint Augustine’s insistence on the sinfulness of human nature. This permitted a view of the secondary law of nations, as with all human-made law, as an adaptation of the principles of natural law to the sinful circumstances wherein humankind lived after the fall from the Garden of Eden. This postlapsarian condition did not allow humanity to relinquish the dictates of natural, or divine, law in the spiritual realm. The law of nations could thus not contradict the dictates of natural law but could allow humans to escape punishment for their transgression against it during their time on earth.Footnote ¹¹¹

In his public lecture on the American Indians, Francisco de Vitoria included some brief reflections on the nature and definition of the law of nations, which at first sight seemed to push it towards a consent-based positive law between sovereign polities.Footnote ¹¹² These and other reflections in his public lectures, need, however, to be read against the background of Vitoria’s more systematic expositions on legal theory in his lectures on the Summa Theologica, although these fail to render a completely consequential and internally consistent treatment. Vitoria took Aquinas’ general theory of laws for a starting point, but made a few significant moves that would inspire later authors and aid them further on the road towards the emancipation of the law of nations from natural law.

Vitoria redrew the boundary between natural law and the law of nations by classifying those principles, rules and institutions that were rational deductions from the first principles of natural reason under natural law. He insisted on the mutable and contingent nature of the law of nations. In De Indis¸ he famously indicated ‘the consent among the greater part of the whole world’ (‘consensus maioris partis totius orbis’) as the source of the law of nations that was binding on all humankind.Footnote ¹¹³ This seemed to establish the majority of sovereign rulers as a universal law-making authority for the community of humankind, peoples or sovereigns. However, this needed to be qualified through Vitoria’s acknowledgement that the international community did not, in reality, act in this way. The law of nations could not easily be changed through common or majority agreement. Common consent was thus less a historical fact than a theoretical presumption that was based on the wide acceptance of a certain institution or rule, and the fact that this institution and rule aided the fulfilment of all law’s higher purpose, the achievement of spiritual well-being and celestial beatitude. The law of nations ‘implemented’ natural law into the concrete conditions of humankind but did not squarely contradict its commands or prohibitions.Footnote ¹¹⁴

A major purpose of Alberico Gentili’s sparse theoretical reflections on the nature of the law of nations in De jure belli (1598) was to place his subject, the regulation of war- and peacemaking, under its umbrella. With this, he wanted to fence off the subject from two directions. On the one hand, placing the jus belli within the ambit of the jus gentium withdrew the regulation of war from the particular jurisdiction of individual states. It was not part of a state’s jus civile. On the other hand, Gentili insisted that the legal regulation of war and its effects was a mere secular matter, which had to be left to secular jurists and was not a matter of concern or expertise for theologians (‘silete theologi in munere alieno’; ‘be silent, theologians, about the business of others’).Footnote ¹¹⁵ This fitted the Protestant political theology that saw a strict separation between the spiritual and secular spheres. Gentili’s famous dictum may be read as a reply to the interferences of Catholic theologians, and in particular the neo-scholastics, in the secular sphere for the higher purpose of spiritual well-being. In reverse, it liberated Gentili in his discussion of war from spiritual concerns.

Gentili equated the law of nations with the law of nature. However, he did not deduce the rules and institutions of war- and peacemaking from the principles of the law of nature through mere rational process. Much to the contrary, his treatise was a grand exercise in exploring a wide array of textual sources – jurisprudential, historical, rhetorical, literary, philosophical, theological – and inductively discovering the rules and institutions of the law of nations from historic as well as current laws, ideas and actions. The underlying foundation of his methodology was the belief that consent among the peoples indicated an approximation of the law of nature.Footnote ¹¹⁶

The key to solve the apparent paradox between Gentili’s equation of the laws of nature and nations and his inductive, humanist methodology was to be found in his Protestant belief that the corruption of human nature through the Fall meant that the direct insight into creation, and into natural law, were irretrievably lost. It was the role of rulers to prevent chaos in the secular sphere by imposing law – hence positive law – a law which ideally approximated natural justice, and divine law. With Gentili, the equation of the law of nations to the law of nature was rather the statement of an ideal than a reality. His treatise on the laws of war- and peacemaking read as an exhortation to rulers, rather than a handbook, a mirror for princes rather than an historical treatise. He did not limit himself to teasing out the law of nations as it was from historical and current practices and scholarly consent but interlaced it with counsel from a perspective of good governance, justice as well as expediency (reason of state). In Gentili’s system, the law of nations was just one guide for statecraft, one which could put only limited restraints on the free arbiter of state, and the pursuance of its preservation and well-being. The law as such was insufficient to outweigh the reason of state and often had to be fortified by the counsels of political wisdom.Footnote ¹¹⁷

Gentili did not expressly define the law of nations in terms of modern public international law: as the consent-based and secular regulation of relations between sovereign states. This step would be most conspicuously set by the Spanish Jesuit Francisco Suárez and the Dutch humanist Hugo Grotius. Both built on the civilians’ triple distinction of jus naturale primaevum v. jus naturale secundarium (= jus gentium primaevum) v. jus gentium secundarium, which the Spanish jurist Fernando Vázquez de Menchaca also had used. For Menchaca, the jus gentium secundarium still spanned the regulation of inter-polity relations as well as the commonalities between different domestic legal systems. In his De legibus, Suárez addressed this ‘dual use’ of the term jus gentium and posited that only its primary use was proper (jus gentium inter se). Moreover, he understood this latter, proper jus gentium as human-made law. It was based on customs, and thus ultimately on agreement. Customs that were widely spread could be considered to apply to all nations on the presumed authority of the community of states, which thus had a kind of legislative authority. This gave the law of nations a measure of autonomy from natural law. Whereas some rules of the law of nations were merely designed to preserve or implement natural law, others could divert from it and were hence mutable. As a theologian, Suárez’ concern remained that of the internal forum, where the validity of all human law ultimately had to be weighed against the higher expressions of divine will and creation, against divine and natural law. This implied that the law of nations might divert from natural law, but not supersede it. It could, however, withhold sanctions from transgressing the precepts or prohibitions of natural law.Footnote ¹¹⁸

In his earliest treatise with regards to natural law and the law of nations, De jure praedae commentarius, the young Grotius deployed the civilian double distinction, classifying the jus gentium secundarium as human-made law.Footnote ¹¹⁹ Although these distinctions were implicit in his theory in De jure belli ac pacis, here Grotius forwarded a more simple scheme. In the sphere of secular relations among states – outside divine law, that is the Decalogue and the law of the Gospel that applied in the spiritual sphere – two laws applied: natural law and the law of nations. Whereas the natural law could apply to both individuals – who found themselves outside the jurisdictional reach of the state in time or space – and states, the law of nations was the sole preserve of states.

Although this dualist scheme was not novel by itself, under Grotius’ legal theory the law of nations reached a new level of autonomy from the law of nature. For Grotius, the law of nations was clearly positive law. It was consent-based. Its major connection to the law of nature was foundational, rather than operational. The binding nature of the law of nations, as of any positive law, was the natural law principle that promises were binding.Footnote ¹²⁰

It was, however, in Grotius’ understanding of natural law and justice that his greatest contribution to the emancipation of the law of nations lies. In both juridical treatises, the Dutch humanist made some significant strides towards the secularisation of the law of nature, and its separation from divine law. In late medieval theology and jurisprudence, divine and natural law were often closely connected. Whereas Gratian largely confounded them with one another, later writers, foremost among them Aquinas, have clearly distinguished them as two categories of law.Footnote ¹²¹ In the Thomistic tradition, divine law referred to God’s direct revelations through history, whereas natural law was inherent in divine reason, as manifested through creation at the beginnings of time. For late medieval canonists, the application of natural law fell within the ambit of ecclesiastical, and papal jurisdiction, as an instance of papal right to interfere in secular legal relations for the benefit of the eternal soul in the afterlife. Vitoria and other representatives of the neo-scholastic School of Salamanca had, however, rejected a claim to universal jurisdiction of the papacy for the upholding of natural law, or the sanctioning of its violation.Footnote ¹²²

Grotius adhered to general (neo-)scholastic theory, but further disentangled natural law from the divine. Firstly, for Grotius, regardless of its origins in divine creation, natural law as a law of reason was intelligible to all rational creatures, regardless of religion. This elevated it into a truly universal law, that all peoples could access, comprehend and apply on the basis of equality. It obviously destroyed any claim of jurisdiction from the papacy, or any particular church. This was the implication of Grotius’ so-called ‘impious hypothesis’ from the Prolegomena of De jure belli ac pacis.Footnote ¹²³ Secondly, Grotius defined the natural rights and obligations that people or peoples derived from natural law as individual and individually enforceable subjective rights (facultas), under the aegis of commutative justice. This justified, under the perspective of natural justice (justum), the pursuance of rights by individuals and states as autonomous actors within their community without regards for the common good. Concerns of distributive justice and the common good were largely relegated to the spheres of divine law (honestum) or political wisdom.Footnote ¹²⁴ This allowed Grotius to reduce the conditions for just war, the major subject of his treatises, to sovereign authority and just cause, casting the third condition from Aquinas’ scheme, righteous intention, largely to the side.Footnote ¹²⁵

In Grotius’ scheme, the law of nature and the law of nations were, however, not the only guidelines for states in their mutual relations. They were the only universal, or potentially universal, laws that were acceptable and binding to all. But to Christians – or at least to those who did not adhere to a radical doctrine of predestination as Grotius did not –Footnote ¹²⁶ who understood nature and natural law as God’s creation, a transgression of natural law was still a sin, which would be judged by God at the end of times. For non-Christians, natural law applied in conscience as well, but they did not understand or accept this as Christians did. This allowed Grotius to read his legal theory back into a – largely neo-scholastic – Christian framework. The law of nations was autonomous from natural law, and the law of nature could be accessed outside faith, but ultimately the law of nature and of nations co-existed, even if they contradicted one another, because they applied in two different spheres. The law of nations was the law of the external forum of secular life on earth that defined the legal effects of the actions of states in their mutual relations. The law of nature also created rights and obligations for states in the external forum, but in many cases they were barred from resorting legal effect, or being enforceable because the law of nations withheld sanction for the transgression of certain natural laws. However, even in these cases, the law of nature continued to apply in the internal forum, in conscience. For most Christians, this implied that adherence to the law of nature would influence their eternal fate.Footnote ¹²⁷