The two crises in this chapter share three main characteristics. They involve territorial (border) conflict that relates to the independence of Ukraine (or, relatedly, the breakup of the Soviet Union), feature an East–West tension, and (as of this writing) do not escalate to a war among the major states. In 2014, after Ukraine attempted to move closer to Europe (i.e., it contemplated an EU agreement and the pro-Russian government fell), Putin annexed Crimea to secure the long-held naval base there. Although done forcefully, there were no military fatalities. In 2022, amidst a fear that Ukraine was again moving closer to Europe (i.e., it looked to be closer to joining NATO and its government became less pro-Russian), Russia invaded Ukraine. It failed to take Kyiv, even though it heavily bombed Ukraine. Russia then withdrew to the east, where a majority of Russian speakers had sought to separate from Ukraine. The United States and the European Union gave weapons and aid that expanded as the war continued. Deaths mounted on both sides. The Russians successfully created a land bridge from the Donbas to Crimea. After his election, Trump attempted to negotiate a settlement that would end the war.

This chapter summarizes the main lessons for diplomacy that we derive from our study. These eight lessons are: 1. A major factor separates the crises that escalate to war from those that do not; in the latter, a strong leader reins in any hard-liners who advocate going to war. 2. Individuals make a difference. 3. Contingency plays a more important role than system structure in determining whether or not a crisis escalates to war. 4. Someone must stand for peace. 5. The secret to preventing war structurally is to find a functional equivalent to war. 6. Norms and rules are important for avoiding war – and, therefore, maintaining peace. 7. War can be avoided; it is not inevitable. 8. The realist concepts of the national interest and balance of power do not always accurately describe the behavior of states.

Chapter 2 examines a period when various European traders attempted to settle in the Amazon by forming local alliances with Indigenous peoples. Although the numbers of these non-Iberian Europeans were tiny, the impact of their partnerships, and the resulting effort by the Portuguese and their allies to eliminate their presence, caused immeasurable damage to native societies in the estuarine areas. By 1640, the Portuguese had expelled the other European interlopers and exacted revenge on the Indigenous allies of their enemies, and started to establish riverbank settlements and plantations. In turn, this led the Portuguese to require labour to service this colonial economy and support their territorial ambitions. They pushed up the Amazon as far as the Tapajós and Madeira rivers to obtain their slaves from the riverbank polities, which gave rise to Belém as the focal point of the Eastern Amazon and marked the beginnings of the formation of a colonial sphere.

July 1914 escalates because of a deterrence failure. Germany and Russia were playing a game of chicken. The kaiser stood firm; he believed that Russia was not prepared for war and would therefore back down. The tsar likewise stood firm; he vowed not to back down again after the Bosnian Crisis – and he thought that Germany would ultimately back down because it would not want to fight the combined power of Russia, France, and the United Kingdom. With neither side yielding, the crisis continued to escalate. A second dynamic contributed to escalation as well. At some point – probably on July 30 – the actors changed strategy. Instead of using coercion to deter their opponent, they started taking coercive measures to increase the likelihood that they would win a war, if one began. Each side mobilized, and mobilization led to war. Beneath all this lay rivalry and the repetition of crises between the major states. Finally, once war broke out between Germany and Russia, the alliance structure caused the war to spread rapidly. From this crisis, we learn many lessons, including that a balance of power and relatively equal military capabilities are associated with war onset; they do not prevent war.

Iceland and the United Kingdom experienced a series of crises that follow a similar pattern. Iceland extended its maritime limits – to preserve more fish for Icelandic vessels and conserve fish stocks. Britain resisted the extension. Both sides escalated their behavior (e.g., issuing threats and coercively harassing each another’s vessels), and Britain ultimately conceded. This chapter covers the 1971–1973 Cod War. It follows the above pattern, but with a somewhat unique twist. In the 1971–1973 episode, domestic politics within both democratic states encourage escalation. Iceland, moreover, threatens to leave the North Atlantic Treaty Organization (NATO) and to evict United States (US) forces from the Keflavik air base. Because of these threats, as well as escalating coercion, NATO mediates, and NATO and the US pressure Britain to concede. Ultimately, this crisis does not escalate to a major-state war because the disputed issue (i.e., maritime limits) lacks sufficient salience and past, similar episodes demonstrate that a nonwar solution exists.

This chapter synthesizes information about the key variables in our framework across all of the cases in our study. We begin with the cases that escalate to war. Here, the patterns among our variables suggest six prominent (nonexclusive) “paths to war”: the hard-liner path, the territorial path, the alliance path, the rivalry path, the bargaining failure path, and the democratic path. The cases that do not escalate to war reinforce the importance of these paths. Actors often avoid war by blocking one or more paths to war. Reining in hard-liners blocks the hard-liner path to war; alliances sometimes restrain actors, rather than emboldening them, thereby blocking the alliance path to war; and norms often provide a way for states to settle the disputed issue at hand. Finally, we discuss the relative importance of system structure. Prior to 1945, domestic politics – particularly, controlling hard-liners – was a more important factor than system structure in the decisions through which actors avoided war. After 1945, however, nuclear weapons reduce the probability of war among the superpowers, often by creating more accommodationists.

The Munich conference notoriously symbolizes appeasement and its failure. The issue under dispute concerns territory – specifically, the Sudetenland. This territorial dispute was initially internal to Czechoslovakia, a disagreement between the Sudetenland Germans and the central government of Czechoslovakia. Eventually, however, the nationalistic element to the dispute brought in the German government. The major powers avoided war because the French and British prime ministers – Daladier and Chamberlain, respectively – forced the Czechoslovakian president, Benes, to accept the peaceful transfer of the Sudetenland to Germany, based on the norm of nationalism (or self-determination). As this case shows, when actors widely agree on the norms through which territory can change hands, the probability of war declines. Nevertheless, this peace was short-lived. Indeed, the afterword to the chapter describes how Hitler invaded Prague shortly thereafter. The Danzig–Poland crises then followed. By that point, Britain and France had abandoned appeasement and shifted to balancing against Hitler; they allied with Poland and gave Hitler an ultimatum to try to stop his invasion. This conventional deterrence failed, and the Second World War began in Europe.

Italian unification ultimately emerges through four wars. This chapter covers the second of these wars (1859–1860). Austria holds sovereignty over territory in northern Italy. Cavour, the prime minister of Piedmont, learns from the first war (1848) that Piedmont cannot defeat Austria – and therefore wrest Italian lands from it – without a powerful ally. He secures an alliance with Napoleon III of France, and at a secret meeting in Plombières, Piedmont and France plot a war. The Italian nationalists argue that the “people” of a nation have a legitimate right to self-rule. The Concert plays no role in this crisis because it does not see the norm of nationalism as a legitimate justification for owning territory. In its view, the norm of dynastic succession (i.e., a king or queen coming to the throne) serves that purpose. The Concert system is therefore biased against the nationalists. The resulting clash of norms increases the probability of war. Nevertheless, territorial issues are generally more war-prone than non-territorial issues, and infusing territorial disagreements with nationalism and identity (or ethnic) claims raises the probability of war further. In the end, the case illustrates well why and how territorial issues lead to war.

This chapter examines the political economy of the hub-and-spokes alliance system in Asia during the Cold War. Focusing on the strategic competition between the United States and the Chinese Communists, it argues that state-building and development were major features of the United States’ efforts to maintain the security of its allies and partners. Because US officials exhibited a heightened concern about the risk of subversion, which could not be contained through military alliances alone, US strategy focused on addressing the perceived causes of its allies’ and partners’ vulnerability. In Northeast Asia, the United States played a significant role in the creation of the developmental state. In Southeast Asia, the United States proved to be less capable or willing to support state-led industrialization, choosing not to do so in the Philippines and failing to do so in South Vietnam. Throughout Asia, containment was as much about economics as it was about military strategy.

Pearl Harbor demonstrates that war can occur when coercion (e.g., economic sanctions) works too well. To investigate this dynamic, we also engage another important, but controversial, question in this case – namely, whether the United States (US) president Franklin D. Roosevelt (FDR) deliberately sought war with Japan as a way to enter the war in Europe. Contrary to some scholars, our analysis concludes that FDR was aware of the total oil embargo that Acheson implemented and that FDR wanted war. Indeed, the US made only one serious attempt to avoid war – the modus vivendi proposal. FDR supported the proposal because he thought it would give the US more time to prepare. Tojo may have entertained the proposal, but he never received it because Chiang Kai-shek and Churchill vetoed it. The latter needed the US to intervene in the war to increase their chances of winning. This is yet another example of alliances promoting war – in this instance, by vetoing a peace proposal. Finally, we consider why Japan was willing to attack the US, even though it knew the US was more powerful.

The Crimean War is an “unnecessary” war. The Concert of Europe crafted the Vienna Note. Because it satisfied all the principal concerns and interests of the major states – and all the representatives of the major states accepted and endorsed it – the Vienna Note should have resolved the crisis. Hard-liners in England, however, undercut the Concert’s proposal and undermined Aberdeen, the accommodationist prime minister. The prospect of British and French support, in turn, emboldened the Ottoman Empire, leading it to declare war on a much more powerful Russia. The Crimean War case is the obverse of the Eastern Crisis (1839–1841) case – in that Aberdeen, unlike King Louis-Philippe, failed to rein in his two main domestic hard-liners. This provides further evidence that domestic politics is a more important factor than system structure in the escalation dynamics of interstate crises.

“Alignment” is an umbrella term to describe a relationship between two or more states that involves mutual expectations of some degree of policy coordination on security issues under certain conditions in the future. The types of alignment explored in this chapter are alliances, thin and thick security institutions, coalitions, and strategic partnerships. The distinguishing features of these alignments are their differing levels of formality and the reason for their creation, or their objectives. Strategic alignments remain one of the dominant means that sovereign states possess to cooperate and coordinate their actions around common threats and political interests. States are either pulled into distrustful relations through security dilemmas or they are obliged to work together to solve common problems. Alliances, security institutions, coalitions, and strategic partnerships offer a variety of ways that states may seek to address security issues, threats, or challenges to their territories or interests.

Some propose that states tie hands by signing alliance treaties. The presence of an alliance treaty increases the audience costs of violating a commitment to defend another state, having the effect of tying hands. This chapter argues that states prefer to keep their hands untied to make it easier to avoid getting drawn into the wrong wars. Accordingly, when states design alliance treaties, they routinely include flexibility language in the treaties that enable them to stay out of conflicts involving embattled allies without violating the treaty, thereby reducing or avoiding the audience costs of abandoning an ally. The chapter demonstrates that all alliances since 1945 include such flexibility language, including alliances signed by the US and Soviet Union/Russia. Further, the chapter demonstrates that in every single post-1945 case when a state allegedly abandoned an embattled ally, the flexibility language of the treaty means that the decision to stay out of the conflict did not technically violate the treaty. On the rare occasions when states want to tie hands more tightly to bolster deterrence, they make verbal statements that de facto reduce the flexibility of the alliance treaty, though such verbal statements are crafted to tie hands minimally.

This chapter explores the justification and legitimisation of war and ‘imperfect’ uses of force both in legal scholarship and diplomatic practice. The Grotian synthesis of ‘just’ and ‘formal’ war entered mainstream scholarship and reached its full explanatory force in the work of Vattel. The resilience of just war in the face of its impracticality among sovereign state in scholarship can, among other, be explained by the fact that the subtle interplay of two conceptions of law in fields of legal application - , gelled well with diplomatic practice. Whereas states applied the jus in bello and jus post bellum with regards to claims to the justice of the war, the just war doctrine remained a common discourse for the justification of resort to war and force and added an instrument to the toolbox of alliances diplomacy.