1. Introduction
To this author’s knowledge, the situation in Gaza is the only contemporary precedent in which a state has argued that the existence of an ongoing armed conflict justifies the use of force without further reference to rules restricting the use of interstate force, or jus ad bellum. This article surveys, but ultimately brackets, questions regarding the general applicability of jus ad bellum to the particular circumstances of GazaFootnote 1 in order to examine the validity of the proposition that the existence of an ongoing armed conflict can alone justify use of force (Section 2). It examines this proposition in the light of the practice and legal opinions of states and international organisations in instances in which force was used during ongoing armed conflicts, particularly the positions put forward by states in Security Council sessions. For the purpose of this article, an ‘ongoing armed conflict’ is one that includes several rounds of hostilities with periods involving tension and occasional skirmishes in between. This position is in line with the broad approach to the scope of applicability of jus ad bellum and jus in bello.Footnote 2 The article then concludes that jus ad bellum continues to apply even in an ongoing armed conflict (Section 3). In Section 4, the article considers the influence that jus ad bellum has had on the ongoing hostilities in Gaza.
The discussion starts by outlining the Israeli position in relation to its use of force in Gaza and the responses of third states and international organisations. It finds that, while hostilities were ongoing in 2023 and 2024, relatively few states took issue with the manner of Israel’s use of force in self-defence and the emphasis on Israel’s entitlement to use force in self-defence declined as the hostilities progressed; however, this position may have shifted following the renewal of hostilities in March 2025. The article then maintains that jus ad bellum continues to restrict state conduct during hostilities and not only at the stage of their commencement; there are substantial challenges that must be overcome for jus ad bellum regulation during hostilities to be effective, one of the main challenges of which is the difficulty of deciding between the different approaches to jus ad bellum proportionality and, consequently, the varying potential limitations to the extent of force that could be used in self-defence. The article outlines such approaches and then demonstrates the differences and the shortcomings of each approach in the circumstances of the Gaza hostilities. In addition, several possible explanations are offered for the finding that the importance of jus ad bellum declined as hostilities progressed, connecting it to certain legal and political factors (including those that complicate the overall applicability of jus ad bellum) and, potentially, the severity of the initial armed attack and the hostilities that have ensued.
2. Overall jus ad bellum applicability
The hostilities in Gaza raise numerous questions of international law. Despite the importance of many other crucial issues that have arisen in connection with the situation in Gaza, the article focuses on one very specific topic: the influence of the underlying armed conflict in Gaza on the application of jus ad bellum. The article, therefore, will not provide clear responses to certain questions that may influence the overall applicability of jus ad bellum to the situation in Gaza, in particular the status of Palestinian statehood and the occupation of Gaza by Israel prior to 7 October 2023.Footnote 3 These issues, and the positions one might adopt in relation to them, ground discussions regarding the applicability of jus ad bellum to Gaza. The importance of Palestinian statehood and the occupation of Gaza are accordingly mapped with a view to underlining the complexity of the applicability of jus ad bellum in the circumstances of Gaza.
The issue of Palestinian statehood could be significant for the applicability of jus ad bellum in that, notwithstanding attempts to expand the scope of the prohibition on the use of force beyond the interstate context,Footnote 4 it is still predominantly considered to require some interstate element, involving state forces, territory and, potentially, nationals and civilian vessels.Footnote 5 In other words, if Palestine is currently not a state, the Gaza situation may lack the interstate element that is required to trigger the applicability of jus ad bellum.Footnote 6 On the other hand, if Palestine is a state and the Gaza Strip forms part of the territory of Palestine,Footnote 7 then Hamas could be perceived as a non-state actor (NSA) that has gained control over Palestinian territory and uses such territory to launch attacks against Israel.Footnote 8
The classification of Israel’s presence and control over Gaza could also be important for the overall applicability of jus ad bellum and the legitimacy of the use of force in self-defence by Israel. In its advisory opinion on the Legal Consequences on the Construction of a Wall, the ICJ cast doubts on the pertinence of the use of force in self-defence in response to attacks that emanate from within an occupied territory.Footnote 9 In a more recent advisory opinion on the Legal Consequences Arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, Including East Jerusalem, in relation to the situation prior to the military operation in response to the 7 October 2023 attack, the ICJ pronounced that ‘Israel’s withdrawal from the Gaza Strip has not entirely released it of its obligations under the law of occupation. Israel’s obligations have remained commensurate with the degree of its effective control over the Gaza Strip’.Footnote 10 While certain states have referred to the existence of occupation as invalidating Israel’s right of self-defence in relation to Gaza,Footnote 11 it is not clear whether the ICJ intended to suggest that the occupation in Gaza and the West Bank is identical when it comes to the applicability of jus ad bellum.Footnote 12
The aforementioned issues significantly complicate the applicability of jus ad bellum in Gaza in the ways summarised, albeit crudely, in the following table:
Table 1. A summary of complicating issues for jus ad bellum applicability in the Gaza context
Admittedly, providing clear answers to these two preliminary issues and deciding which is the correct legal construction for the applicability of jus ad bellum are essential to understand fully the relevance of jus ad bellum to the circumstances of Gaza. Discussing jus ad bellum without fully resolving these issues may thus create a sense of unease with the average international lawyer. However, many states have referred to the right of Israel to use force in self-defence, without fully engaging with these questions.Footnote 13 In addition, as the only modern case in which a state has attempted to avoid the constraints of jus ad bellum based on the existence of an ongoing armed conflict, the Gaza situation may become an important reference point on this question of ‘displacement’.Footnote 14 It therefore merits a separate analysis of this argument and the practice and statements of other states in relation to the relevance of the armed conflict to the applicability of jus ad bellum and its application.
3. Ongoing armed conflict
This section will present, explain and analyse the Israeli position regarding the justification to use force as part of an ongoing armed conflict, and will then continue to review relevant state practice, ultimately arguing that this position finds little to no support in the sources of international law.
3.1. Israeli position
Following the rounds of hostilities in Gaza in 2008–09 and 2014, and about a month after the attack of 7 October 2023, the Israeli government released its legal position on the various issues connected to these hostilities in official publications (the 2009 Report, the 2015 Report and the 2023 Report, respectively). These publications are indispensable for our purposes, as they present the Israeli position regarding the jus ad bellum aspects of the Gaza situation in detail. In the 2009 Report it was stated:Footnote 15
[T]his resort to force occurred in the context of an ongoing armed conflict between a highly organised, well-armed, and determined group of terrorists and the state of Israel. The Gaza Operation was simply the latest in a series of armed confrontations precipitated by the attacks perpetrated without distinction against all Israeli citizens by Hamas and its terrorist allies. In fact, over the course of this conflict, Israel conducted a number of military operations in the West Bank and the Gaza Strip, to halt terrorist attacks. … Even apart from the eight years of ongoing armed conflict, which justified Israel’s resort to force both previously and during the Gaza Operation, Hamas’ intensified armed attacks on Israel and its citizens during 2008 independently justified Israel’s response to defend its citizens.
The 2015 Report followed the same line, with the following argument:Footnote 16
Hamas’s attacks leading up to the 2014 Gaza Conflict were thus part of a larger, ongoing armed conflict. But even if one were not to consider the 2014 Gaza Conflict part of a continuous armed conflict justifying Israel’s use of force both previously and during this time, Hamas’s armed attacks against Israel in 2014 would independently qualify as an armed attack triggering Israel’s inherent right of self-defence.
The 2023 Report similarly highlighted the context of an ongoing armed conflict:Footnote 17
The heinous attacks launched by Hamas and Islamic Jihad against Israel on October 7, 2023, which left over 1,400 Israeli and foreign nationals murdered and thousands more wounded, and the continuing attacks since then, took place in the context of an ongoing armed conflict between Israel and Hamas and other terrorist organizations in Gaza. For this reason, in particular, legally speaking, these attacks do not necessitate an analysis of the conditions under which Israel may resort to the use of armed force (the jus ad bellum).
Israel has argued, therefore, that the existence of an ongoing armed conflict permits a state to use force on an ongoing basis. For the purpose of this article, this position will be referred to as the ‘displacement’ approach, as it essentially presumes that the regulatory force of jus ad bellum is displaced because of the applicability of jus in bello during an armed conflict. More precisely, Israel does not maintain that jus ad bellum was entirely inapplicable, but that Israel’s role as defender was determined at the commencement stage of its ongoing armed conflict with Hamas and the Palestinian armed groups, and therefore Israel’s use of force beyond this stage of the armed conflict does not require a separate justification. This argument is similar to the approach of several scholars whereby if the initial armed attack justifies launching a ‘war of self-defence’, the victim state is entitled to use force throughout such ‘state of war’ without jus ad bellum imposing any further restrictions.Footnote 18
In both the 2009 Report and 2015 Report (but not the 2023 Report), Israel formulated its position in a somewhat indirect way and connected ‘displacement’ with alternative arguments regarding the specific circumstances of the relevant round of hostilities.Footnote 19 Furthermore, Israel has not relied on ‘displacement’ in other forums (including the Security Council sessions that addressed the 2008–09 and 2014 rounds of hostilities in Gaza or in the 2006 hostilities in Lebanon, in which Israel justified its use of force independently as self-defence based on the prevailing facts and not the existence of an ongoing armed conflict).Footnote 20 In the course of the round of hostilities that followed the 7 October 2023 attack, Israel relied on self-defence or its ‘right to defend its people’ and likewise preferred to engage with the specific circumstances that brought about its forcible response, namely the 7 October 2023 attack.Footnote 21 Nevertheless, while Israel has not relied on ‘displacement’ outside its aforementioned publications on the Gaza situation, several scholars and commentators have relied on ‘displacement’ (or a variation of it)Footnote 22 to justify Israeli attacks in other areas, such as Syria and Lebanon.Footnote 23
3.2. Critical analysis
Israel’s position assumes that there exists an overlap between jus ad bellum and jus in bello during armed conflicts, as a result of the broad scope of the applicability of both of them. For jus ad bellum, the prohibition on the use of force is predominantly construed broadly, to apply to any use of armed interstate force.Footnote 24 Quite similarly, jus in bello is perceived predominantly as extending from the first use of interstate force and beyond the area in which hostilities take place and beyond the cessation of hostilities, until the general close of military operations.Footnote 25 Such broad applicability of both fields will result in an overlap between their applicability following the use of armed interstate force.Footnote 26 Note, however, that for both jus ad bellum and jus in bello there are scholars who interpret their scope of applicability narrowly so that their commencement is subject to a gravity threshold and that, for jus in bello, such applicability would end following the cessation of hostilities (particularly if the parties concluded a formal ceasefire).Footnote 27 These positions are highly controversial and, in any event, their adoption will limit the overlap between jus ad bellum and jus in bello only to periods in which hostilities are taking place.
In Israel’s opinion, the result of the applicability overlap between jus ad bellum and jus in bello is that the latter prevails, while the former ceases to impose any restrictions on the parties to an armed conflict once an armed attack has occurred. This is clearly demonstrated by Israel’s most recent assertion in the 2023 Report, whereby ‘[legally speaking] the context of an ongoing armed conflict … do[es] not necessitate an analysis of the conditions under which Israel may resort to the use of armed force (the jus ad bellum)’.Footnote 28 Under the jus ad bellum regime of the UN Charter, this position could be sustained only if its proponents could establish that this is the appropriate manner in which the scope of the right of self-defence should be interpreted. However, as provided below, no such support could in fact be found.
First, the ‘displacement’ of jus ad bellum during armed conflicts finds no support in the relevant treaty provisions, specifically the prohibition on the use of force or the right of self-defence.Footnote 29 The preamble, purposes and drafting history of the UN Charter all point in the opposite direction, denoting an expansive interpretation of jus ad bellum, limited only by the narrow exceptions enshrined in the Charter,Footnote 30 while indicating the maintenance of international peace and security as the primary purpose of the Charter.Footnote 31 Furthermore, furnishing a party to an armed conflict with unlimited discretion to use force is not in line with the obligation of states to resolve their disputes peacefully, which has been interpreted as imposing duties on states during armed conflicts.Footnote 32
The foregoing is also reflected by the legal developments that led to the adoption of a jus ad bellum regime that is divorced from the meaning of ‘war’. In essence, such developments were designed primarily to ensure that the applicability of jus ad bellum (and jus in bello, for that matter)Footnote 33 is completely objective and factual, and to avoid any arguments that the intention of the parties to engage in ‘war’ plays any significant role in the applicability of jus ad bellum.Footnote 34
Moreover, in so far as the overall structure and purpose of international law are concerned, previous discussions regarding the interaction of jus ad bellum and jus in bello focused on concerns regarding the application of the latter. Specifically, it was argued that jus ad bellum would undermine the equality of belligerents under jus in bello by distinguishing between lawful and unlawful parties to an armed conflict (according to their status under jus ad bellum) and adjusting the operation of jus in bello accordingly.Footnote 35 In order to avoid the devastating consequences this would have for jus in bello, the fields were perceived predominantly as independent and separate.Footnote 36 In other words, when the potential influence of jus ad bellum on jus in bello applicability was discussed, it was generally agreed that the applicability of jus in bello should not be influenced by jus ad bellum, to avoid undermining the object and purpose of jus in bello. However, if arguments of ‘displacement’ are accepted, this would undermine the ability of jus ad bellum to play its crucial role in the maintenance of peace and security, which is unacceptable for the same reasons.Footnote 37 Put differently, the interaction between jus ad bellum and jus in bello should not be interpreted in a manner that would render their regulatory power practically meaningless for extended periods.Footnote 38 This result is further established by the universally accepted principle whereby preference would be given to an interpretation that maintains the effectiveness of the relevant provisions.Footnote 39 According to the latter principle, an interpretation that results in the continuous operation of both jus ad bellum and jus in bello is preferable in so far as it allows for their simultaneous applicability.
Yet, the most compelling reason for rejecting the ‘displacement’ approach is that it finds no support in the practice and legal opinions presented by states and international organisations, a key element for ascertaining the position of customary international law and potentially informing the interpretation of the jus ad bellum provisions of the UN Charter.Footnote 40 No other state except for Israel has argued that the right of self-defence continues to justify the use of force throughout an armed conflict. Furthermore, when Egypt attempted to rely on its alleged state of war with Israel as justification for the restriction of shipping in the Suez Canal in 1951,Footnote 41 the Egyptian position was rejected by the vast majority of states participating in the Security Council discussion, including Israel.Footnote 42 Another relevant example is the Israeli attack on the Osirak nuclear facility. In this instance, Israel relied, among other things, on the fact that Iraq considered itself to be in a state of war with Israel as evidence of the dangers posed to Israel by the Osirak facility, justifying Israel’s attack in self-defence.Footnote 43 This argument was rejected predominantly on a factual basis, with participants (which included states as well as non-state entities entitled or invited to participate in the session, such as the International Atomic Energy Agency, the Arab League and the Palestine Liberation Organization (PLO)) denying the military nature of the facility.Footnote 44 Nevertheless, some participants directly rejected Israel’s purported unlimited right to use force against military objectives based on a supposed state of war with Iraq,Footnote 45 or rejected Israel’s right to use preventive self-defence during such state of war.Footnote 46 In doing so, these states explicitly or implicitly rejected ‘displacement’ by dismissing Israel’s attempt to broaden the availability of the use of force during a state of war: explicitly, for those states that directly rejected ‘displacement’, by maintaining that merely being in a state of war was insufficient to justify an Israeli attack;Footnote 47implicitly, as the concept of pre-emptive self-defence – a broad interpretation of the right of self-defence to include circumstances in which the preventive attack is not connected to a specific threat – is in many ways identical to that of ‘displacement’. If it were to be accepted, it would result in overstretching the concept of self-defence, doing away with the requirement of the occurrence of an armed attack, and rendering the assessment of any limitations on the use of force in self-defence (which are connected with the armed attack) virtually impossible.Footnote 48
On the other hand, there are many examples where, despite the existence of an ongoing armed conflict, directly involved and third states and international organisations referred to jus ad bellum to justify the use of force in the specific circumstances prevailing at the time. These examples include, inter alia, the armed conflicts between Israel and the Arab states,Footnote 49 India and Pakistan,Footnote 50 and Armenia and Azerbaijan.Footnote 51
3.3. Ongoing Gaza conflict
In the light of the above, it is submitted that there is sufficient evidence to support the rejection of the ‘displacement’ approach put forward by Israel with respect to the jus ad bellum legality of its operations in Gaza. While the armed conflict in Gaza between Israel, Hamas and other Palestinian armed groups could be classified as an ongoing armed conflict in which jus in bello continues to apply beyond the actual hostilities, this alone does not invalidate the requirement to provide independent jus ad bellum justifications for the use of force during such armed conflict.Footnote 52
Given the breadth of evidence for the rejection of the ‘displacement’ of jus ad bellum, Israel’s hesitancy when it comes to reliance on ‘displacement’Footnote 53 (at least in so far as previous rounds of hostilities in Gaza are concerned) is understandable and is in line with the findings of this article. Yet, despite its shaky foundations, Israel still maintained this position with respect to the most recent use of force in Gaza. This is particularly interesting given that, as mentioned above, there are other arguments that Israel could have raised that would completely deny the applicability of jus ad bellum.Footnote 54 Why, then, might Israel be continuing to invoke the ‘displacement’ approach?
First, it seems that Israel preferred a position that supports the applicability of jus ad bellum to the armed conflict in Gaza, as this position enables Israel to act and provides overall justification for its operations in Gaza. Still, Israel’s position on the aforementioned overall applicability issues – namely, the status of Palestinian statehood and the Gaza occupationFootnote 55 – is that the Palestinians have yet to attain statehood and that Gaza is not occupied.Footnote 56 It is therefore difficult to surmise what is the legal construction that led to Israel’s conclusion that jus ad bellum is applicable to Gaza. Several possibilities could be suggested: that Israel perceives every use of cross-border force as triggering the applicability of jus ad bellum;Footnote 57 that Israel views Gaza as a quasi-state, ruled by Hamas, thereby triggering jus ad bellum applicability;Footnote 58 that Israel views the scope of jus ad bellum obligations as extending beyond the use of interstate force;Footnote 59 that Israel, as well other states, has not considered the complicating factors that exist in the Gaza situation. In any event, some of these possibilities may contradict Israel’s positions on other issues, such as Palestinian statehood, and without a clear pronouncement on this matter, it is impossible to determine the actual legal construction that forms the basis of Israel’s position.
Second, it is possible that by advancing this argument in relation to Gaza, Israel is actually expressing its perceived legal basis for continued operations in other (interstate) arenas, such as Lebanon and Syria. Israel has been involved in numerous attacks against targets in these two states and ‘displacement’ has been put forward by commentators as a potential justification for such attacks.Footnote 60 The fact that Israel has so far avoided officially relying on an ongoing armed conflict or ‘displacement’ when it comes to any area other than Gaza may serve to weaken this conclusion but could also demonstrate Israel’s general lack of faith in the ‘displacement’ approach.
Third, Israel’s narrow reading of the limitations imposed by jus ad bellum would also invalidate the continuous need to justify its maritime blockade of the Gaza Strip, which, in turn, justified the restrictions Israel that enforced on the passage of goods into the Gaza Strip.Footnote 61 In its analysis of the legality of the blockade, the Turkel Commission (which was established by the Israeli government to examine the legal aspects of the 2010 Gaza Flotilla incident and, in doing so, assessed the legality of the Israeli maritime blockade of Gaza) relied primarily on provisions of jus in bello and the law of the sea, without analysing the legality of the blockade under jus ad bellum.Footnote 62 Still, if we assume that jus ad bellum applies in the circumstances of the situation in Gaza, then the inclusion of ‘[t]he blockade of the ports or coasts of a state by the armed forces of another state’ by the General Assembly, as an example of acts that could qualify as aggression, indicates that the imposition of the maritime blockade falls within the ambit of jus ad bellum.Footnote 63 From this perspective, by dismissing the continued relevance of jus ad bellum during the ongoing armed conflict in Gaza, Israel is provided with a blanket justification of all the measures it would employ, including the imposition of a maritime blockade, at least in so far as jus ad bellum is concerned.
Fourth, the ‘displacement’ approach provides a way to avoid addressing more sensitive issues that are associated with other threshold arguments which address the overall applicability of jus ad bellum: namely, the status of Palestinian statehood and the territory of Gaza.Footnote 64 As Israel does not recognise the state of Palestine,Footnote 65 it makes perfect sense for it to refrain from bringing the issue of Palestinian statehood to the fore. In addition, Israel disagreed with the pronouncement of the ICJ in its advisory opinion on the Legal Consequences of the Construction of a Wall regarding the irrelevance of the right to use force in self-defence in response to attacks originating from occupied territory.Footnote 66 It has also objected to the findings of the latest advisory opinion by the ICJ,Footnote 67 in which the Court decided that Gaza remains occupied for some purposes.Footnote 68 Therefore, it is highly unlikely that Israel will rely on any alleged occupation of Gaza to justify its actions. Under these circumstances, Israel’s reliance on jus ad bellum, including its ‘displacement’ in previous rounds of hostilities, allows it to circumvent the discussion of some difficult topics that may complicate the applicability of jus ad bellum.
4. Ongoing hostilities
As established in the previous section, the Israeli position regarding the nature of the interaction between jus ad bellum and jus in bello during the ongoing armed conflict in Gaza is unsupported by international law. Assuming that jus ad bellum does continue to apply during armed conflicts, this section will discuss the manner of jus ad bellum operation in the round of hostilities that commenced following the Hamas attack on 7 October 2023.
4.1. Israel’s position
In the 2009 and 2015 Reports Israel argued, as an alternative justification for its ‘continuous armed conflict’ argument, that it had used force in Gaza not only to halt and repel ongoing armed attacks but also to avert the ongoing threats posed by Hamas and other Palestinian armed groups in Gaza.Footnote 69 Israel emphasised that the constant firing of rockets and mortar from Gaza to Israel and their intensification had compelled the Israeli response.Footnote 70 Furthermore, in the 2015 Report, Israel maintained:Footnote 71
[T]he proportionality of force used in self-defence depends upon the amount of force required to repel attacks and eliminate the continuing threat. Figures regarding the number of casualties (either looked at as a whole or as compared to losses incurred on the other side), do not, in and of themselves, point to a disproportionate use of force. In responding to Hamas’s attacks, Israel used no more force, for no longer a period than necessary to accomplish its objective: protecting Israel from incessant, illegal terrorist attacks.
Similarly, throughout discussions in the Security Council of the Gaza hostilities that commenced in October 2023, Israel relied on self-defence or its ‘right to defend its people’.Footnote 72 It should be noted that while Israel did refer explicitly to self-defence, it did not rely on Article 51 of the UN Charter in doing so.Footnote 73 Furthermore, during the Security Council discussions and in the 2023 Report, Israel also made direct comparisons between the 7 October 2023 attack and the 9/11 attack, and highlighted statements by the leadership of Hamas vowing to repeat such attacks.Footnote 74
Yet, whereas in previous rounds of hostilities in Gaza, Israel stated that its operations were a response to the ongoing threat posed to it by Hamas,Footnote 75 during the discussions of the hostilities that followed the 7 October 2023 attack, Israel may have framed the objectives of its response to this attack before the Security Council more expansively. These objectives went beyond merely halting and repelling an ongoing attack (for example, because of the continuous bombing of the Israeli civilian population and the holding of hostagesFootnote 76) or even the prevention of future attacks, to also include the far-reaching goal of the complete destruction of Hamas (or its capabilities).Footnote 77 Moreover, according to Israel, the defeat of Hamas and its refusal to release the Israeli hostages it held justified the renewal of hostilities in Gaza in 2025. On March 2025, in a Security Council session on the renewal of hostilities by Israel after an almost two-month long ceasefire, the Israeli representative stated the following:Footnote 78
We stand firm in our commitment to return the hostages and defeat Hama[s]. … We will bring home every last hostage. Hamas has refused to release our hostages and repeatedly rejected all the offers, both by the United States and the mediating countries, even for the period of Ramadan. And thus, the return to fighting is a necessity.
It should be noted that, at least according to some sources, Hamas agreed to release all the Israeli hostages in return for a permanent ceasefire and the withdrawal of Israeli troops, while Israel has either rejected these terms or demanded further measures to ensure that Hamas does not retain its control over Gaza.Footnote 79 If these reports are correct, then it is not just the holding of Israeli hostages that rendered ‘the return to fighting … a necessity’, but the fact that Hamas meant to stay in power in Gaza and would not release the hostages unless Israel consents to this condition. Put differently, following the 7 October attack, Israel has signalled that the existence of Hamas as a military force (or even as a political entity in general, if this is Israel’s intention in indicating the complete annihilation of Hamas as an objective) constitutes a threat to it. This is distinguished from particular actions precipitated by Hamas (such as the firing of rockets) that were specified as constituting an ongoing threat to Israel in previous rounds of hostilities.
Numerous states and international organisations which participated in the Security Council sessions during the end of 2023 and 2024 referred to the availability of a right of self-defence to Israel (or to Israel’s ‘right to defend itself’) in the circumstances following the 7 October 2023 attack, in line with ‘international law’ and/or ‘international humanitarian law’.Footnote 80 In addition, while many states referred during this period to necessity and proportionality in their statements, only a few such statements could reasonably be interpreted to refer to jus ad bellum necessity and proportionality,Footnote 81 as limitations imposed by customary international law on the use of force in self-defence.Footnote 82 Still, it is possible that the reference to ‘international law’ is alluding to additional limitations imposed on the use of force in self-defence in accordance with customary international law, which include necessity and proportionality.Footnote 83
On the other hand, a substantial number of states and international organisations have rejected Israel’s right to respond to the 7 October 2023 attack from the outset, citing various reasons such as the illegality of Israel’s use of force to capture Gaza in 1967, the illegality of the Israeli occupation, the right of the Palestinians to self-determination and the unavailability of self-defence against an occupying power, or simply by characterising the Israeli actions in Gaza as ‘aggression’.Footnote 84 For those states that maintained that Israel had either violated jus ad bellum from the outset or that jus ad bellum does not regulate the circumstances of the Gaza conflict, jus ad bellum did not play any additional role during the hostilities themselves.
In the course of the Security Council discussions of the Gaza hostilities in 2023 and 2024, only five states which referred to Israel’s right of self-defence during the hostilities have at least implied that Israel has exceeded its limits.Footnote 85 Before the General Assembly, four more states maintained or implied that Israel’s use of force in self-defence went beyond what is permissible in accordance with jus ad bellum.Footnote 86 In any event, as the hostilities progressed during 2024, the emphasis on the availability of Israel’s right of self-defence declined.Footnote 87
On March 2025, Israel renewed hostilities in Gaza, ending a two-month ceasefire, and suspended the passage of humanitarian aid into Gaza for a period of more than two months.Footnote 88 In the general discussion of April 2025, the trend of the decline in the number of references to the right of self-defence continued.Footnote 89 Quite importantly, the renewal of hostilities seemed to cause a shift in the position of several Western states which had previously supported Israel’s right of self-defence. It began by the United Kingdom and France signalling their unease with the renewal of hostilities before the Security Council,Footnote 90 and culminated in official statements by the UK, France and Canada.Footnote 91 These statements were also followed by comments of the German ChancellorFootnote 92 which, while not attaining the official character of the preceding statements, may also imply that Germany’s position regarding the operation in Gaza was being reconsidered.
4.2. Self-defence during hostilities
At the outset, it should be emphasised that the continued applicability of jus ad bellum even during hostilities is supported by practice and opinio juris of states.Footnote 93 This is established, inter alia, by the response of states to the Israeli invasion of Lebanon in 2006Footnote 94 and by letters sent by states to the Security Council in armed conflicts such as Vietnam,Footnote 95 Iran-Iraq,Footnote 96 and the Falkland Islands.Footnote 97 Furthermore, in the 2009 and 2015 Reports, Israel essentially accepted that if its argument regarding the irrelevance of jus ad bellum during a continuous armed conflict is rejected, then jus ad bellum remains relevant following the commencement of hostilities.Footnote 98
As with the concept of armed conflict, the relevant treaty provisions (including supporting obligations, such as the duty to peacefully settle disputes) indicate a willingness to increase the scope of jus ad bellum applicability, and contain no language to support the cessation of such applicability during hostilities.Footnote 99 Yet, the existence of hostilities and their specific characteristics – including their varying intensity levels, the participating actors, and the involvement of the international community – may all influence the manner of the scope of jus ad bellum constraints that are imposed on the parties to an armed conflict. In addition, the continued applicability of jus ad bellum during armed conflicts results in an interaction between the general rules and exceptions of jus ad bellum, on the one hand, and the rules of jus in bello. As a universal principle of law, rules are generally applicable whereas exceptions must be interpreted narrowly, to apply only during the specific circumstances that trigger their operation and only for such time as these circumstances remain relevant.Footnote 100 For jus ad bellum, this means that the prohibition on the use of force (as well as other related general obligations such as the duty to peacefully settle disputes) governs the legal relationship between parties to an armed conflict, unless and for such time in which one of the parties to an armed conflict establishes the existence of circumstances that permit it to use force.Footnote 101 As already mentioned, the two main exceptions that receive broad acceptance are enshrined in the UN Charter: the right of self-defence and authorisation by the Security Council according to a Chapter VII resolution.Footnote 102
If we accept the broad position for the applicability of jus in bello, an armed conflict may exist in the absence of hostilities, and may indeed include several rounds of hostilities.Footnote 103 In order to conform with jus ad bellum, hostilities involving the use of collective ‘means of injuring the enemy’Footnote 104 or, in other words, the use of armed force, require one of the parties to the armed conflict to demonstrate that it is entitled to use force according to the aforementioned jus ad bellum exceptions. In the round of hostilities following the 7 October 2023 attack, Israel has argued on numerous occasions that it is entitled to use force in self-defence.Footnote 105 Therefore, the analysis in this section will focus on issues that are related to the application of self-defence during the hostilities that followed the Hamas attack of 7 October 2023.
The availability of the right of self-defence is predicated on the occurrence of an ‘armed attack’.Footnote 106 Depending on the factual characteristics of the particular use of force, an armed attack could be classified as imminent,Footnote 107 ongoing or completed.Footnote 108 However, even if self-defence is available, the use of force itself is further restricted by the customary requirements of necessity and proportionality.Footnote 109 These concepts are highly disputed, and fully resolving these disputes is beyond the scope of this article. For the purpose of this article, necessity will be treated as considering whether force could be used, obligating states to resort to force only as a last resort and arguably limiting their choice of targets.Footnote 110 In that sense, the existence of hostilities may support a claim that force is the only measure that could be used in response to an armed attack. In other words, when an armed attack is ongoing, it may serve by itself as evidence that the use of force is necessary.Footnote 111 Yet, following the cessation of hostilities, and for as long as the right of self-defence is still available, a state that wishes to renew such hostilities must demonstrate that the (defensive) objective of its operation could be achieved only through the use of armed force.Footnote 112
Proportionality, which regulates the extent of force that could be used, is more relevant to the analysis of the use of force during ongoing hostilities. Scholars distinguish between two main competing notions of proportionality.Footnote 113 The ‘quantitative’ understanding of proportionality requires that the force that was used would not exceed the effects caused by the original armed attack.Footnote 114 On the other hand, interpreting proportionality as a ‘means-end’ concept would entail that such force could not exceed what is required to achieve a defensive purpose.Footnote 115 As mentioned above, there is disagreement among scholars regarding the correct approach for the determination of jus ad bellum proportionality,Footnote 116 and the position of statesFootnote 117 and the ICJFootnote 118 on this issue has been somewhat ambiguous. This indeterminacy, particularly when it comes to the position of states and international organisations, limits the ability to provide a concrete and definite verdict in terms of jus ad bellum proportionality, which is crucial for the efficiency of jus ad bellum regulation during hostilities. Furthermore, regardless of the actual legal position that most accurately reflects the state of international law, both approaches have their practical shortcomings.
For ‘quantitative’ proportionality, it has been argued that it involves a complex analysis of various effects that are not easily measured or compared.Footnote 119 In addition, it is difficult to quantitatively ascertain the effects of an ongoing armed attack during hostilities, as such effects can continue to materialise over time.Footnote 120 For example, if state A invades state B, the effects of the invasion, including the death of the residents of the territorial state and the destruction of its infrastructure, could not be perceived as terminated just because state B decides to forcefully respond to the invasion. ‘Quantitative’ proportionality may therefore be unwieldy and result in the exclusion of certain effects that occur regularly.
The aforementioned complexity is reinforced by the fact that the temporal classification of an armed attack is not always a clear-cut exercise. For example, the issue of occupation of state territory was specified as potentially bringing about the continuation of an armed attack.Footnote 121 The topic is still debated, but it should be noted that in 1973, when Egypt and Syria used force against Israel, some third states relied on a right of the Arab states to recover territory that was unlawfully occupied by Israel in 1967 as justification for the attack.Footnote 122 Nevertheless, in other instances, such as the Argentinian invasion of the Falkland/Malvinas IslandsFootnote 123 and the Iraqi invasion of Kuwait,Footnote 124 territorial reclamation arguments were highly disputed.Footnote 125 In addition, for our purposes the continuation of an armed attack may also include the firing of rockets on the civilian population of the victim stateFootnote 126 and, arguably, the capturing or holding of nationals of the victim state, if we adhere to the contested doctrine that allows states to rescue nationals who were captured and are being held in other states or territories.Footnote 127 When it comes to the capturing of nationals as part of an invasion of state territory, it could be maintained that this is distinguished from the capturing of nationals abroad, as the former could be perceived as directly connected, as an extension of the effects of the invasion itself and, consequently, of the original armed attack.Footnote 128 Furthermore, certain scholars maintain that several attacks could be accumulated, so that the response in self-defence encompasses several relatively smaller forcible incidents.Footnote 129 While this latter theory is not necessarily part of the lex lata, it could also, in practice, potentially lead to a modification of the scope of the armed attack.
In comparison, ‘means-end’ proportionality is more flexible in that it is not bound to the exact effects of an armed attack but to the attainment of an objective; yet the scope of this objective is not always clear. While the halting and repelling of an armed attack is the most commonly cited defensive objective,Footnote 130 it is suitable only for dealing with ongoing armed attacks (and, in this case, the challenges of deciding whether an attack is in fact ongoing are also relevant), but not with imminent or completed attacks.Footnote 131 For these latter types of armed attack, it has been suggested that, under some circumstances, the ‘defensive’ objective may also include the prevention and deterrence of threats or further attacks.Footnote 132 Nevertheless, unlike a response to an imminent armed attack that has yet to occur, which requires establishing the existence of an actual threat of an immediate attack,Footnote 133 the conditions that would lead to the expansion of a ‘defensive’ objective to include future-oriented goals beyond the halting and repelling of an armed attack are not always clear.
While states have formulated their objectives in this sense in the past, the scope of the threat that they intended to address remained ambiguous. A classic example of a defensive operation with broad objectives in the pre-Charter era is the Second World War, where the Allies stated that their war aims included the ‘unconditional surrender’ of Axis states.Footnote 134 These objectives were also set as the foundations of the United Nations which, at the time, was used to define the group of states that supported the Allies and their cause in the Second World War, and later became the name of the new international organisation that was established following the war. This is embodied, inter alia, by the inclusion of Article 107 in the UN Charter.Footnote 135 Nevertheless, it should be noted that the Second World War predated the UN Charter, which greatly contributed to the shaping of contemporary jus ad bellum and was and remains up to this day exceptional in its intensity and scope. Furthermore, the Allies’ expansive war objectives were not set at the commencement of the war, but in 1943, and they were naturally influenced by the manner and the progression of the hostilities.Footnote 136 A more recent example of an operation with future-oriented goals is the invasion of Afghanistan following 9/11, in which both the UK and the US responded to a completed armed attack which caused substantial damage, and framed their objectives as designed to prevent threats and deter future attacks.Footnote 137 The invasion initially received broad supportFootnote 138 and was seen by scholars as a significant milestone in the development of a more permissive jus ad bellum regime.Footnote 139 While the Afghanistan operation continued for more than a decade, it was not always clear that it was framed as an act of self-defence throughout that entire period.Footnote 140 Another recent example of an operation which supposedly involved relatively wide-ranging objectives is the campaign of the international coalition against ISISFootnote 141 in which some states relied more explicitly on the threat posed by ISISFootnote 142 whereas others merely cited the right of self-defence.Footnote 143 This campaign started, among other reasons, as a response to the ongoing ISIS attack on Iraq, but ISIS was largely driven out of Iraq in 2017; the operation continued mostly on Syrian territory,Footnote 144 and included large-scale destruction that went mostly unnoticed by the international community. This led O’Meara to argue that in these two latter situations – in which the Security Council acknowledged that the situation constitutes a threat to international peace and security and referred to the right of self-defenceFootnote 145 (or some ambiguous variation of itFootnote 146) – the constraints of jus ad bellum on the use of force in self-defence could have very little practical effect.Footnote 147 Unlike the Second World War, the two other aforementioned cases concern the use of force against NSAs which is, in itself, a disputed area in jus ad bellum. However, all three cases may be similar in that they are all associated with a response to an armed attack of a relatively significant scope in terms of its scale and gravity.
The ICJ has stated that ‘it cannot reach a definitive conclusion as to the legality or illegality of the use of nuclear weapons by a state in an extreme circumstance of self-defence, in which its very survival would be at stake’.Footnote 148 This statement has sparked a lively debate, but in essence the ICJ pronounced that, at least in so far as jus ad bellum is concerned, a state could be permitted to use the most extreme means at its disposal when its very survival is at stake.Footnote 149 Other scholars have also cited the effects of the initial armed attack, coupled with those of the ensuing hostilities and the existence of reasonably foreseeable future attacks, as potentially influencing the scope of the objective.Footnote 150
Nevertheless, the breadth of the debate on the application of these standards, in both scholarship in the legal opinions of states, is insufficient and, as a result, the attainment of such future-oriented objectives could be elusive. A significant question is whether such future-oriented standards refer only to imminent threats that have materialised as impending attacks or whether they refer to more general threats posed by the existence of an adversary that is opposed to the state, more closely akin to a right of pre-emptive self-defence (which is still widely considered as contrary to jus ad bellum).Footnote 151
In the light of the above, the main problem of ‘means-end’ proportionality lies with the difficulties inherent in determining the scope of and conditions for the attainment of a defensive objective, which is at the heart of ‘means-end’ proportionality. The aforementioned ambiguity risks providing states with an almost unlimited margin of appreciation when it comes to jus ad bellum Footnote 152 that would practically amount to the ‘displacement’ of jus ad bellum during hostilities (or even during the entire armed conflict). While the magnitude and scope of certain types of attack and hostilities may, at some specific point in time, provide a state with broad freedom in the execution of its defensive operation, the protective role of jus ad bellum should not be discarded off-handedly and – in line with the object, purpose and nature of jus ad bellum – should be sensitive to the prevailing circumstances. If this supposed development of jus ad bellum into a more permissive regime flows from the invasion of Afghanistan following 9/11, the dire consequences of the intervention in Afghanistan (namely, the regaining of control by the Taliban 20 years later)Footnote 153 should also serve as an appropriate reason to rethink the amount of freedom and margin of appreciation we should grant to states while engaging in defensive operations.Footnote 154 Unlike jus in bello, which focuses on specific attacks, jus ad bellum is better placed to allow states to review a military operation as a whole, not only with respect to the initial circumstances that led to its commencement but also when it comes to the manner in which force is used.Footnote 155 This could potentially be utilised to provide additional protection for the civilian population, as jus ad bellum allows states to rely on general figures and statistics in their appraisal of a military operation, and to reflect on the compatibility of the overall effects of the operation with a defensive objective and/or the effects of the initial armed attack to which it responds.
The difficulties encountered by both models of proportionality and the ambivalence of the positions expressed by states and international organisations could be mitigated potentially by the adoption by some scholars of a ‘mixed’ model, which relies predominantly on ‘means-end’ proportionality but leaves space for ‘quantitative’ proportionality, by prohibiting a response that is ‘markedly asymmetric’ when compared to the effects of the initial armed attack.Footnote 156 While this model is apparently more balanced and provides a comprehensive assessment of the effects of a defensive response, the standard of ‘marked asymmetry’ remains indeterminate, and the examples of practice that have been cited to establish the existence of this standard are mainly responses to armed attacks with relatively limited initial effects.Footnote 157 In so far as the ‘marked asymmetry’ standard is contextual, it should also be affected by the defensive purpose of the operation. Therefore, it is unclear how ‘marked asymmetry’ could be utilised to compare a defensive response to armed attacks of a more substantial scale. The challenge of a ‘mixed’ model is even greater when it comes to comparing the harmful effects of the operation with the benefits of fulfilling its defensive objectives, as it is virtually impossible to compare concrete effects with presumed benefits.Footnote 158
In summary, while jus ad bellum continues to play a role during ongoing hostilities, its application raises numerous challenges, in particular because of the debate regarding the nature of jus ad bellum proportionality and the shortcomings of the different approaches to proportionality. These challenges will be demonstrated through the discussion of the Israeli use of force in Gaza in response to the 7 October 2023 attack.
4.3. Ongoing Gaza hostilities
While there are different approaches to proportionality, they all seem to be mindful to some extent of the effects of the initial armed attack. Therefore, a cautious survey of such effects, and of the effects of the operation launched by Israel in response, is provided below. While it is acknowledged that the actual numbers and the classification of numerous targets are highly disputed, and that there are substantial challenges when it comes to the verification of some of the data, there could be no doubt that this round of hostilities is unprecedented in its intensity and the scope of destruction. The figures presented below are therefore a mere indication of the intensity and gravity of the initial and ongoing effects of the armed attack and the Israeli response.
According to a UN fact-finding report, during the 7 October 2023 attack, more than 1,200 people were killed (of whom at least 809 were civilians), 14,790 were injured and 252 were abducted as hostages into the Gaza Strip.Footnote 159 Furthermore, thousands of rockets were fired and extensive damage was caused to military facilities and to civilian infrastructure in towns and cities that were subjected to the attack.Footnote 160 Following the 7 October 2023 attack, Hamas continued to launch thousands of rockets into Israeli territory, causing further destruction and the deaths of 18 people (as in May 2024).Footnote 161 Furthermore, Hamas and other Palestinian armed groups continue to hold Israeli hostages and, in May 2025, at least 58 Israeli hostages were still held captive in the Gaza Strip.Footnote 162 In so far as the situation in Gaza is concerned, as at 28 May 2025, the Hamas-affiliated Gaza Ministry of Health stated that 54,084 people had been killed and 123,308 were wounded in Gaza as a result of the Israeli response to the 7 October 2023 attack.Footnote 163 Moreover, the Israeli operation has reportedly caused widespread hunger and malnutrition (with Israel’s decision to suspend the entry of humanitarian aid exacerbating these effects)Footnote 164 and the destruction of civilian infrastructure, including at least 92 per cent of housing units that have been either damaged or destroyed.Footnote 165 By March 2025, Israel estimated that it had eliminated approximately 20,000 Hamas fighters during the hostilities in Gaza.Footnote 166 Notwithstanding the foregoing, no serious attempts were made to provide figures that distinguish between the destruction of military and civilian infrastructure in Gaza.Footnote 167
Because of the significant gravity of the 7 October 2023 attack, unprecedented in the Israeli–Palestinian conflict in terms of casualties and damage within Israel, there is no dispute that its magnitude is sufficient to constitute an armed attack.Footnote 168
In relation to the various notions of jus ad bellum proportionality discussed in the previous section, Israel’s position reflects a ‘means-end’ (or at least a ‘mixed’Footnote 169) approach, requiring the use of force in self-defence to conform with a defensive purpose.Footnote 170 In previous rounds of hostilities, Israel defined the defensive purpose as a response to the ongoing threat posed by Hamas and the Palestinian armed groups in Gaza.Footnote 171 In discussions regarding the hostilities following the 7 October 2023 attack, Israel went even further, stressing that the purpose of the operation is the complete destruction of Hamas and its capabilities.Footnote 172 This broad formulation of a defensive objective goes even beyond that of the US and the UK when they invaded Afghanistan, but that invasion essentially attempted to achieve the same objective, which is the complete dismantling of Al-Qaeda and the overthrow of the Taliban regime.Footnote 173
A ‘means-end’ approach is understandably attractive to Israel in that, as mentioned above, it is far more flexible and may provide states with a very broad margin of appreciation to use force during the ensuing hostilities.Footnote 174 If Israel’s goal of the complete destruction of Hamas is accepted as the defensive objective of its operation, then Israel may continue to use such force as is required until the achievement of ‘absolute’ or ‘total’ victory over Hamas.Footnote 175 On the one hand, the massive scale of the 7 October 2023 attack, the continuation of rocket and mortar fire following the attack, the fact that Hamas does pose an ongoing threat to Israel and that its leaders have vowed to annihilate Israel and repeat these attacksFootnote 176 may all justify the setting of a broad defensive objective. The comparison by Israel between the 7 October 2023 attack and the 9/11 attack by Al-Qaeda on the World Trade Centre is highly significant in this case. The 7 October 2023 attack, exceptional in terms of the gravity and scale of the invasion by Palestinian NSAs onto the territory of Israel, could definitely be dubbed the ‘Israeli 9/11’.Footnote 177 Yet, attaining an ‘absolute victory’ is, as Israel’s then Defence Minister Yoav Gallant has said,Footnote 178 perhaps not entirely possible or, at least, a highly complex task with unspecified parameters.Footnote 179 Achieving ‘absolute victory’ could entail, for example, the occupation of Gaza for an unspecified duration to completely dismantle the Hamas organisational structure, wipe it out as a military force or even a political entity, and prevent Hamas from rebuilding itself, at least in Gaza.Footnote 180 Such an expansive interpretation of the use of force in self-defence would arguably enable Israel to renew hostilities even following extended ceasefires, for as long as the overall objective of removing Hamas from power in Gaza is not achieved. Certain statements by high-ranking Israeli officialsFootnote 181 (while bearing in mind the uncertainty regarding their actual influence on Israeli policyFootnote 182) and Israel’s refusal to clarify its policy regarding the ‘day after’ in GazaFootnote 183 should, at a minimum, raise serious suspicions and concerns regarding the ‘defensive’ objective of the Israeli operation. Together with the widespread destruction in Gaza, the desirability of discarding the additional layer of protection provided by jus ad bellum by allowing Israel uninhibited discretion to use force in self-defence for an unlimited duration could be questioned.
The law is not entirely clear on this issue, but a more limited conception of the defensive objective may greatly affect the permissible scope of the Israeli response. For example, the operation’s defensive objective could be more directly connected to the 7 October 2023 attack. Since the Hamas leadership expressed its intention to repeat such attacks,Footnote 184 Israel’s desire to dismantle Hamas’s military capabilities that were used to launch the attack could potentially be perceived as more directly addressing the imminent threat that Israel faced following the 7 October 2023 attack. According to this objective, the Israeli operation would naturally be more restricted in so far as jus ad bellum is concerned as it would be required to demonstrate the connection between its chosen targets and the 7 October 2023 attack. Regardless, it could still include, for example, the Hamas leaders who were responsible for planning and launching the attack, the units that were used in the attack, Hamas’s rocket arsenal and operators, its drone capabilities, and so forth. It is also doubtful that under a relatively more limited characterisation of the defensive objective of the operation, Israel would be entitled to renew hostilities on a whim, particularly if it could be demonstrated that the elements within Hamas that were involved in the planning and execution of the 7 October 2023 attack had already been dealt with by March 2025. Deciding whether it is Hamas as a whole, or specific Hamas elements that were instrumental in the launching of the 7 October 2023 attack, that pose an imminent threat to Israel is therefore an essential question that greatly affects the means that were available for Israel’s defensive response under a ‘means-end’ approach to proportionality.
In any event, even under an expansive view of the defensive objective of its operation, Israel would be hard pressed to justify a complete suspension of the passage of humanitarian aid into Gaza. Admittedly, this suspension was not assessed under jus ad bellum by participants in the relevant Security Council sessions.Footnote 185 Still, since Israel has in the past treated the suspension of the passage of goods into Gaza as a blockade,Footnote 186 its legality must also be reviewed simultaneously according to the limitations of jus ad bellum, namely the requirements of necessity and proportionality,Footnote 187 in addition to the rules of jus in bello which have been central to other states’ commentary (and the investigations of the ICC).Footnote 188 From this perspective, at least concerning Israel’s complete suspension of the passage of humanitarian aid for 11 weeks without any consideration of the needs of the civilian population of Gaza, it seems that such conduct has exceeded even the most lenient interpretation of ‘means-end’ proportionality, based on the dire consequences that such suspension has had on the humanitarian situation in Gaza.Footnote 189 Generally speaking, if we agree that jus ad bellum is applicable to the situation in Gaza, then the blockade imposed by Israel on the Gaza Strip throughout the operation must also be continuously assessed and evaluated under the lens of jus ad bellum, together with other forcible means that Israel has used during its operation. At least according to a ‘means-end’ approach, this means ensuring that the operation does not exceed its defensive objective.
In so far as ‘quantitative’ and ‘mixed’ proportionality are concerned, their shortcomings in the circumstances of the Gaza hostilities that commenced following the 7 October 2023 attack are demonstrated by Van Steenberghe’s analysis of the jus ad bellum legality of the Israeli response.Footnote 190 While seemingly espousing a ‘mixed’ model of proportionality,Footnote 191 Van Steenberghe proceeds to compare the effects in terms of casualties on both sides.Footnote 192 However, in doing so, Van Steenberghe does not grapple with the scope of the defensive objectives of the Israeli operation; nor does he take into account arguably ongoing effects (that is, the missile and mortar barrages and the capturing of hostagesFootnote 193). Van Steenberghe’s analysis of jus ad bellum proportionality also does not calculate the potential implications of the Israeli limitations on the passage of humanitarian aid.Footnote 194 If we do consider these measures to fall within the ambit of jus ad bellum,Footnote 195 then the effects that were directly caused by such measures should also be part of the calculation of the quantitative effects, but isolating these effects might not be straightforward. Moreover, Van Steenberghe does not consider previous instances in which states responded to an initial armed attack with substantial effects, where a significant inequality between the effects of the armed attack and the response was accepted by a substantial number of states (examples include the aforementioned invasion of Afghanistan and the campaign of the Coalition against ISISFootnote 196). Therefore, despite the primacy of the ‘means-end’ analysis in a ‘mixed’ model of proportionality, Van Steenberghe highlighted its ‘quantitative’ aspects without engaging with the actual objectives of Israel’s operation or with the application of the ‘marked asymmetry’ standard in cases where the initial armed attack was particularly grave. Having said that, there is no doubt that the effects of the Israeli response far outweigh the effects of the initial armed attack in terms of casualties and destruction and, therefore, the force that was used would most likely be perceived as excessive in accordance with ‘quantitative’ proportionality. For ‘mixed’ proportionality, as a result of the aforementioned challenges faced by a ‘means-end’ approach to proportionality, without clarifying the manner of application of ‘marked asymmetry’ in instances of armed attacks with particularly grave effects, at least up to the suspension of the passage of humanitarian aid by Israel in March 2025 it was relatively difficult to determine whether the Israeli response was excessive. Yet, as mentioned before, even a very expansive definition of a defensive objective has boundaries, which were arguably exceeded in the case of the Gaza situation.
In any event, while jus ad bellum did play a role during the Gaza hostilities, it is acknowledged that such role was relatively limited.Footnote 197 For states and international organisations that argued that self-defence was inapplicable or that Israel has violated it from the outset, it did not play any role in further restricting Israeli conduct, which was either unregulated by it or constituted a continuous violation of it. On the other hand, the vast majority of states and international organisations that referred to the availability of self-defence to Israel did not rely on the limitations imposed by jus ad bellum on the use of force in self-defence in order to restrict or otherwise criticise Israeli conduct. This conclusion still holds even if we consider the shift in the position of some Western states, which used language that might allude to jus ad bellum, although without conducting a detailed assessment of the jus ad bellum legality of the Israeli conduct.Footnote 198
The refusal of most participants who referred to the availability of self-defence under these circumstances to engage directly with the legality of Israel’s response under jus ad bellum – in particular, as a result of its severe effects compared to previous rounds of hostilities in Gaza – is somewhat surprising, and therefore merits some clarification. Nevertheless, the interpretation of state silence is a complex task that requires a careful analysis of state conduct in its context. It raises both doctrinal and factual problems that are relevant to international law as a whole. From a factual point of view, there are numerous reasons for states to choose to express themselves on a given topic. Such differences in motivation reinforces the doctrinal problem, which concerns the legal significance or weight we give to state silence.Footnote 199 In the case of the Gaza hostilities, two possible yet conflicting explanations are therefore offered below.
On the one hand, the silence of states could be explained as a reluctance to provide clear opinions on the issues at hand. As mentioned before, the legal basis for the applicability of jus ad bellum is not completely clear in this case.Footnote 200 While this did not prevent states and international organisations from articulating their positions regarding jus ad bellum, it could result in their unwillingness to provide a comprehensive position on jus ad bellum that may involve complex legal analysis of sensitive issues. On the other hand, focusing on jus in bello allows a state to express its concerns regarding the legality of Israeli conduct during the hostilities, and circumvent these issues. There could also be other political or legal reasons for states to refuse to engage with jus ad bellum, including the fact that at least some states (such as the US, UK and Germany) may be legally liable for providing arms to Israel in the knowledge that Israel is using these weapons to commit internationally wrongful acts.Footnote 201 This may also explain the suspension of export licences of arms which were used in Gaza, for example by the UK and French governments.Footnote 202
The alternative explanation is that those states and international organisations that explicitly agreed with the availability of self-defence, without fully commenting on the broad objectives put forward by Israel and did not later explicitly revise their jus ad bellum stance, may indeed believe that the constraints of jus ad bellum are more permissive during the hostilities that have ensued. This explanation is seemingly in line with a presumption of acquiescence when it comes to state silence, which becomes even more plausible when a state has already expressed its opinion on a certain topic.Footnote 203 According to this theory, the silence of states that have previously referred to the availability of Israeli self-defence could be interpreted as a continuous conviction that Israeli actions in Gaza are in line with jus ad bellum. In other words, if broad defensive objectives are accepted, they may affect the scope of force which could be used in relation to such objectives so that the limitations that would otherwise be imposed by jus ad bellum during the hostilities are marginal. This reasoning feeds back to the centrality of the 9/11 attack in the development of a more permissive jus ad bellum regime and the comparison between 9/11 and the 7 October 2023 attack. Yet, in comparison with the Afghanistan invasion and the campaign against ISIS, the Gaza hostilities do not deal with the collective efforts of a coalition of states against a threat that was defined by the Security Council; nor has the Security Council referred to the right of self-defenceFootnote 204 in any of the relevant resolutions concerning the Gaza hostilities.Footnote 205 Regardless, this explanation could assist in distinguishing between the current hostilities in Gaza and the 2006 Israeli invasion of Lebanon or previous rounds of hostilities in Gaza, where the effects of the initial attack were considerably less grave, and states expressly criticised the Israeli action under jus ad bellum.Footnote 206 It is also in line with the precedent of the campaign of the Coalition against ISIS, which also caused great destruction and likewise was not widely condemned in terms of jus ad bellum.Footnote 207
As mentioned above, due caution must be exercised in basing this potential conclusion on state silence, as it may constitute part of a trend that would weaken the role of jus ad bellum during certain types of hostilities in which maintaining the protection provided by jus ad bellum would be most crucial for the maintenance of international peace and security.Footnote 208 Furthermore, while this analysis may have been more cogent before March 2025, it seems that the renewal of hostilities by Israel and the suspension of the passage of humanitarian assistance did cause a certain shift in the positions of prominent Western states, suggesting that even state silence has its limits. With the passage of time and the increased calls for the immediate cessation of hostilities, this interpretation of state practice, which would provide Israel with the right to use force for an unlimited duration, seems less likely. It is therefore surprising that many states that initially supported Israeli self-defence did not formulate their statements in a manner that more clearly rejects the overall basis for the Israeli operation (thereby prompting its immediate cessation).
5. Conclusion
While the hostilities in Gaza raise numerous questions of international law, this article has focused on the influence of the underlying armed conflict and hostilities in Gaza on the applicability and application of jus ad bellum. This is because the Gaza situation is the only modern precedent where a state has argued that it is entitled to use force in self-defence throughout an ongoing armed conflict, and also as the current ongoing hostilities provide an example of a response by a state to a highly severe and grave armed attack by an NSA.
The article rejected the argument that jus ad bellum is ‘displaced’ during an ongoing armed conflict, because of the lack of support for this approach in the sources of international law, in particular, the scarcity of supporting practice, express rejection of this approach on several occasions, and the numerous instances in which states invoked jus ad bellum despite the existence of an underlying armed conflict.
If jus ad bellum continues to impose constraints on state conduct during hostilities, and there are no other factors particular to Gaza to preclude the applicability of jus ad bellum, it becomes necessary to examine what the jus ad bellum constraints are. However, these constraints are not always clear, particularly as a result of the existence of several competing approaches to jus ad bellum proportionality that might determine the extent of force that could be used throughout the hostilities. The analysis of the brief statements of states and international organisations on the jus ad bellum aspects of the Gaza hostilities creates even more confusion regarding the correct approach, and may require a complex analysis of the significance of state silence. In this sense, the Gaza hostilities constitute yet another example of the complexities of extracting legal conclusions from the statements and practice of states and international organisations.Footnote 209 While this is a pertinent issue for public international law in its entirety, it is especially prevalent in jus ad bellum because of the vagueness and ambiguity regarding the legal opinion of stakeholders on the most contentious jus ad bellum issues, including the debate on jus ad bellum proportionality.
For jus ad bellum to fulfil its important role in limiting the overall effects of a defensive operation, additional clarity on these issues is required. Such clarity could be facilitated by encouraging states and international organisations to be more explicit about their legal understanding perhaps, for example, by referring contentious jus ad bellum questions to the ICJ for an advisory opinion, as matters that are closely related to the maintenance of international peace and security, the primary purpose of the Charter.Footnote 210 Advisory proceedings before the ICJ would not only provide us with a pronouncement by the principal judicial organ of the UN,Footnote 211 but would also encourage states and other stakeholders to provide their legal opinion on these issues.Footnote 212
Acknowledgements
This author wishes to thank Professor Kimberley Trapp and Dr Megan Donaldson for their assistance in the writing of this paper as well as Professor Claus Kreß for the inspirational exchanges on matters relating to the jus ad bellum aspects of the armed conflict in Gaza.
Funding statement
Not applicable.
Competing interests
The author declares none.
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