Does Israel Have the Right to Defend Itself?

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This is a deceptively simple question. It has several possible answers, each of which rests on different (and highly contested) assumptions. In this post I will try to explain what these possible answers are, and what are their implications. I don’t myself know what the ‘correct’ answer here is. It is not my intention to argue for one. I should not be taken as doing so, even implicitly. Rather, my point is simply that, as applied to Israel, Palestine and Gaza, the jus ad bellum is a mess. Israel’s war against Hamas in Gaza is not, legally, an open-and-shut, clear-cut situation. We do have such clear situations – it is reasonably clear, in my view, that the US and UK committed aggression when they invaded Iraq in 2003, as it is even clearer that Russia committed aggression against Ukraine. But Gaza is not such a case.

There are two further arguments that I want to make.

First, that many who think there is a single, clearly correct answer to the question whether Israel has a right to self-defence do so simply because the answer fits their prior narratives and worldviews. They find that particular answer (yes it does; no it does not) comfortable and obviously correct, indeed so obviously correct that any opposing argument can, for them, only be made in bad faith. Some of the proponents of these obvious answers are themselves acting in bad faith, because they are rabid partisans for one of the parties to the conflict or attention-seeking opportunists, especially in the social media cesspits. But most are not. Most people with very firm views on this question, who believe that it (and others) has obvious answers, are good people acting in good faith. However, their thinking is, for various reasons, warped by motivated reasoning and confirmation bias, and this leads them to replace complexity with simplicity. This is just human nature.

To be clear, I am not here claiming that some kind of perfect objectivity is possible, nor am I arguing that Israeli or Palestinian voices don’t deserve to be heard because they are inherently not objective. I am also not arguing that I am a paragon of objectivity, happily pontificating here to our readership. Like everybody, I too suffer from my own biases. All I am saying is that partisanship in the Israeli/Palestinian conflict is not one of them, for whatever that’s worth. Neither Israel nor Palestine are my tribe, nor do I belong to any other allied political, religious or ideological tribe. The only conflict that I care viscerally about is the one in the former Yugoslavia (although probably less so as time goes by), in a way that the pro-Palestinian/pro-Israeli tribespeople almost certainly do not. But it is precisely the bitter experience of the former Yugoslavia, where crazy nationalism and parallel realities still run rampant, that has given me a partial inoculation against the kind of polarization that Israel/Palestine so easily provoke – or at least so I would like to believe. This is just to explain as clearly as possible where I’m coming from.

My second argument is that the jus ad bellum is so complex, uncertain and contested as it applies to Israel and Gaza that it actually has very little useful to say. This is a strange confession for an international lawyer. But there are some problems for which the law does not have solutions. In my view, Israel/Gaza is one of them when it comes to the jus ad bellum. International law does have solutions when it comes to the jus in bello, the law of armed conflict, but its rules are very contextual, fact-specific and generally operate on a tactical level. They are not about the big picture, for the most part. By contrast, the jus ad bellum is about the big picture, but as I’ll explain below its indeterminacy here is such that there is little it can usefully do. International law does say other things very clearly – that Israel is systematically violating the human rights of Palestinians, that it is denying the Palestinian people the free exercise of their right to self-determination so that they can establish their own state, that the continuing of the occupation is a violation of self-determination, that promoting and protecting the activities of settlers in the West Bank is unlawful for multiple reasons, and so on. But the jus ad bellum, in my view, simply does not provide clarity for the current conflict in Gaza.

Morality and ethics, on the other hand, do in my view provide clearer answers. Morally, the only way in which Israel can justify its continuing military action in Gaza, with such horrible consequences for its civilian population, is by some kind of ‘lesser evil’ utilitarian calculus: if the lives of innocents it takes now serve the cause of saving more innocent lives in the future. With each passing day, with each dead baby in a Gazan hospital, that justification becomes more difficult to make. I, at least, fail to understand how the Israeli government can today reasonably claim that – speculatively, in the future – it will have saved more innocent lives than it has already taken.

But that’s morality, not the law (or it’s very debatable whether this is the law, as I will explain later), and I am very willing to listen to contrary views. Here, as I said, I want to examine the legal question of whether Israel has a right to self-defence, in response to the atrocity perpetrated by Hamas on 7 October. By self-defence I mean solely that notion as defined in Article 51 of the UN Charter, not some more open-ended political concept. The issue, in other words, is not whether Israel broadly speaking has the right to defend its own people (the core function of any state, any organized political community). Rather, the issue is whether, in conducting its military operation in Gaza, Israel is exercising its inherent right to self-defence within the meaning of Article 51, as bounded by the customary requirements of necessity and proportionality.

Having (hopefully) clarified the scope and nature of my task here, I will now proceed to examine the following points in turn:

  • Self-defence applies only if the prohibition on the use of force is engaged, which depends, inter alia, on the statehood of Palestine
  • Self-defence against Hamas if Palestine was a state or the prohibition on the use of force was otherwise engaged
  • Self-defence against Hamas in occupied territory
  • No self-defence against self-defence
  • Different conceptions of ad bellum proportionality

Warning: this is a long post!

Self-defence applies only if the prohibition on the use of force is engaged

Let’s start with this crucial point, one which Dapo and I examined on the blog regarding previous iterations of the Gaza conflict (see here and here). Self-defence is an exception to the prohibition on the use of force in Article 2(4) of the Charter. The exception does not apply at all if the prohibition itself is not engaged, and that prohibition is at least prima facie inter-state in nature. Consider the most obvious example, that of a state using force against rebels on its own territory. Even if thousands of people were killed in some kind of uprising, and the state sensibly decided that it needed to use armed force to defend itself, this would not be self-defence in the Article 51 sense. Rebels are not protected by the prohibition on the use of force in Article 2(4), which only applies in international relations, and the state doesn’t need Article 51 to justify using force against them. Nor would its response be limited by necessity and proportionality as the jus ad bellum uses the terms. There is simply no jus ad bellum internum. Maybe there should be one, but there isn’t one.

How is this relevant to Gaza? Because it is not obvious that the Article 2(4) prohibition is even engaged when Israel uses forces in Gaza, since the status of that territory is so uncertain. What is certain is that Hamas, the non-state armed group, is not as such either bound by, or protected by, Article 2(4). When Hamas uses force against Israel, or when Israel uses force against Hamas, Article 2(4) is just not applicable. Accordingly, without more, Article 51 does not apply either. Article 51 would apply only if, in order to use force against Hamas, Israel indirectly uses force against some entity that was protected by Article 2(4). Again, the exception to a prohibition cannot logically apply if the prohibition itself does not apply.

Imagine a scenario in which, in response to the 7 October attack, Israel only used force for a few days in order to kill Hamas fighters on the territory of Israel itself. This would not be self-defence in the meaning of Article 51 of the Charter, because the prohibition in Article 2(4) would not be engaged at all when Israel uses force against a non-state actor on its own territory. Or, imagine a scenario in which, in response to the 7 October attack, Israel destroyed a boat on the high seas, flying no state’s flag, which was full of Hamas fighters. This would again not be self-defence in the meaning of Article 51 of the Charter, since the prohibition on the use of force is not engaged at all if Israel fires at such a vessel outside any state’s territorial sea. Note that this is not the same question as whether armed attacks in the sense of Article 51 can be committed by non-state actors (I will turn to it below). The point here is simply that Article 51 is not some kind of freestanding rule that can apply without Article 2(4).

So, what if Israel uses force against Hamas in the territory of Gaza? Do Articles 2(4) and 51 even apply? The answer to this question would clearly be yes only in one scenario – if Palestine already existed a state, and Gaza was its sovereign territory. The prohibition on the use of force would then apply between Israel and Palestine. Israel would need to rely on Article 51 not to justify using force against Hamas, but to justify using force on Palestine’s territory without Palestine’s consent. In other words, if Palestine was a state, the situation would be exactly the same as with, say, the 2006 war between Israel and Hezbollah in Lebanon, or with frequent Israeli strikes against Hezbollah now on the territory of Lebanon, or against other Iran-affiliated groups in the territory of Syria. In all of these cases Israel has been using force on the territory of other states without their permission, and could only potentially justify doing this on the basis of Article 51.

But, obviously, this raises the question of whether Palestine has achieved statehood. For most of the other states in the world, the answer is yes. For Israel and quite a few other states supporting it, the answer is no. There is legally no doubt whatsoever that the Palestinian people have the right to self-determination, which entails that there ought to be a state of Palestine. But there is doubt as to whether the ought has become an is, because the state of Palestine lacks the effectiveness criteria normally required to establish a new state. So, the basic dilemma here is whether the international community has, through collective action, such as the recognition of Palestine’s non-member observer state status in the UN General Assembly, compensated for Palestine’s deficits in other respects. This is again a question with no obvious answers, on which reasonable people can disagree, and which also has implications elsewhere – for my part I will only say that the case for Palestine’s statehood is substantially stronger today than it was 15 years ago. The core difficulty, however, is that Israel, the state using force on Palestine’s territory, doesn’t recognize Palestine’s statehood.

Another way out of this problem would be to argue that the Article 2(4) prohibition on the use of force protects self-determination units, not just states, and that Palestine is one such unit even if it has not yet attained statehood. That is an argument that is much more difficult to make, and I will leave it at that. There is no clear, generally accepted authority supporting this proposition. What is clear, however, is that Article 2(4) is not engaged simply because Israel is acting outside its territory. It would be engaged only if Israel, in using force, violated the sovereignty of some other state (see my ship on the high seas example above). I would respectfully disagree with Professor Mary Ellen O’Connell’s recent argument here on the blog in that regard; the road to Article 51 and its limits goes through Article 2(4), and that prohibition exclusively (or near-exclusively) applies to states.

Bottom line: Article 51 self-defence would most likely be relevant only if we accepted that Palestine already is a state. Paradoxically, this means any formal invocation by Israel of self-defence when it uses force against Hamas could be taken as some kind of implicit recognition of the idea that the prohibition on the use of force is engaged, and that it needs to justify breaching it – in some sense supporting the statehood of Palestine. If, however, Article 2(4) was not engaged, Article 51 would not apply at all. This doesn’t mean that Israel would be prohibited from using any force against Hamas, just that the jus ad bellum would be irrelevant in assessing the legality of that use of force, which could only be judged based on the rules of IHL and human rights law. The position would be no different than if there was fighting between Israel and a non-state actor on Israeli territory.

Self-defence against non-state actors if the prohibition on the use of force was engaged

Let’s assume the legally clearest situation, which is that Palestine has already achieved statehood. Any use of force by Israel on Palestine’s territory without Palestine’s permission would then need to be justified by relying on Article 51. The core problem here, as readers will be aware, is whether armed attacks in the sense of Article 51 can be committed by non-state actors. This is a question that has endlessly been discussed in the literature and here on the blog. I will not expound on it here in detail. Suffice it to say that states and scholars are divided into two camps. The first, restrictivist camp argues that, like Article 2(4), self-defence in Article 51 is purely inter-state in nature, and that only states can commit armed attacks. The second, expansionist camp argues that state practice has affirmed the position that self-defence can apply to armed attacks by non-state entities, as e.g. with the US use of force in Afghanistan after the 9/11 attacks by Al Qaeda.

I don’t want to get into which of these two camps is today somehow the ‘majority’ position. Both views are entirely in the mainstream. I am on the record as arguing that, as things stand, the jus ad bellum is indeterminate on the question of whether non-state actors, whose conduct is not attributable to a state, can commit armed attacks in the sense of Article 51 of the Charter, and I am happy to continue sitting on my fence on this point. What I think can fairly be said is that the expansionist camp has been gaining more traction in recent years. But the restrictivists are very much fighting back – recall how one of the reasons the United States gave for vetoing the first draft UN Security Council resolution on Gaza was precisely because the resolution didn’t expressly affirm Israel’s right to self-defence, which it didn’t do precisely because many states on the Council were not comfortable with the idea that self-defence can, in law, apply to attacks by non-state actors.

Israel (and the United States) are, of course, firmly in the expansionist camp. If the position of that camp was taken as correct, then Israel would undoubtedly have the right to defend itself against Hamas on the territory of Palestine. If, however, the views of the restrictivist camp were taken as correct, then Israel could not use any level of force against Hamas in Gaza without Palestine’s consent, unless it could be argued that the conduct of Hamas was attributable to Palestine. (Theoretically, this might be doable under the rule set out in Article 9 of the ILC Articles on State Responsibility.) Imagine a scenario in which, in response to the 7 October attack, Israel only conducted limited aerial strikes in Gaza against Hamas fighters, killing a few civilians incidentally, and conducted (very risky) targeted ground operations to rescue hostages. Even such a minimalist campaign would be unlawful under the restrictivist argument in the absence of attribution – a position that I, as a matter of policy, find difficult to accept, but one which is legally more than tenable. See, in that regard, Mary Ellen’s post I referred to above.

Self-defence against a non-state actor in occupied territory

This brings me to another problem. Arguments have been made in the literature, based partly on an ambiguous paragraph in the ICJ’s Wall advisory opinion, that self-defence is inapplicable in situations of occupation. Imagine the following scenario: in Russian-occupied territories of Ukraine, Ukraine organizes a group of partisans who, on Ukraine’s behalf, attack Russian armed forces. Would Russia have the right to self-defence here? No – that right simply doesn’t apply, at least because Ukraine is the defending state and is trying to liberate its own territory, i.e. there is no self-defence against self-defence. The jus ad bellum has nothing to add here beyond the already clear position that Russia has violated Article 2(4).  

But what if a group of partisans organized spontaneously, with no involvement by Ukraine and with Ukraine even disavowing them, and they attacked Russian forces – would self-defence apply then? And what if the partisans attacked Russian forces in Russian territory, rather than in occupied territory, but returned to the latter after their operations were over? Would Russia have the right to self-defence?

In this second scenario, my view is that the key point is whether the partisans, or some other non-state group, are acting on Ukraine’s behalf or are not. If they are not, i.e. they are not conceivably exercising Ukraine’s right to defend itself against Russia, then we’d be in a situation that’s no different than the general problem of armed attacks by non-state actors. That Russia is already present in Ukraine ad bellum unlawfully doesn’t change that analysis.

In sum, I doubt there is anything particularly special about the operation of self-defence in an occupied territory, although I acknowledge that there have been different views on this in the literature. Self-defence is an ad bellum category, occupation an in bello one, and it is unclear to me why there should be any direct link betweeen them. Even if some special considerations did apply, there remains the incredibly controversial issue of whether Gaza remains occupied by Israel, on which views again differ. And even so any inapplicability of self-defence to hostilities in an occupied territory would not entail a prohibition on the use of armed force – the only regulatory regime would be IHL.

No self-defence against self-defence

This brings me to the argument recently made on Opinio Juris by Dr Ralph Wilde. That argument is, well, a bit wild, especially because it is presented with such unshakeable certainty as to its correctness. I can’t really do it justice here, but, as far as the jus ad bellum is concerned, it more or less boils down to the following sequence of propositions and conclusions:

  1. Israel is engaging in a continuous armed attack in the sense of Article 51.
  2. The 7 October operation by Hamas was a defensive action against the continuing Israeli armed attack. Dr Wilde accepts that the 7 October operation was a violation of the jus in bello. But nonetheless, he argues, Hamas’ actions were still acts of ad bellum self-defence.
  3. Therefore, because there can be no self-defence against self-defence, Israel’s actions in Gaza are not self-defence and are ipso facto unlawful. QED.

Each of these points is highly problematic, even if we accepted arguendo much of Dr Wilde’s preceding account as valid. On (1), note, dear reader, that Dr Wilde never actually tells us who the victim of this attack exactly is. Is it the state of Palestine (which if it exists would definitely be protected by the Article 2(4) prohibition on the use of force, and could also rely on Article 51 self-defence)? Or, is it the Palestinian people (where the applicability of Article 2(4), and consequently Article 51, is much more problematic, as I explained above)? Note, again, that there can be no armed attack by Israel if the prohibition on the use of force is not engaged at all vis-à-vis the alleged victim of the attack. Note also that Dr Wilde doesn’t even mention the relevance of Palestine’s (contested) statehood for any of these issues. Again, legally the clearest situation would be if the state of Palestine was already in existence, and on that basis Israel’s continued occupation could conceivably amount to an armed attack against that state – but note all of the assumptions built into this.

On (2) Dr Wilde’s argument really falls apart. Let’s say there is already a state of Palestine, and that Israel’s occupation of Palestine is an armed attack against it. But is Hamas acting on Palestine’s behalf, so that it could exercise Palestine’s Article 51 right to defend itself? The only representatives of the state of Palestine that seem to be acknowledged as such by the international community – the Palestinian Authority in the West Bank – are not exactly aligned with Hamas. Nor have they endorsed the 7 October operation. Alternatively, if there was no state of Palestine, would Hamas be acting on behalf of the Palestinian people, who somehow have an Article 51 right to defend themselves? Note how Dr Wilde talks about the Palestinian people right to resist the Israeli occupation, even by using force – something I am happy to accept in principle. But is that right to resistance the same right as self-defence in Article 51 of the Charter, which only speaks of attacks against members of the United Nations, i.e. states? And even if it was, how on Earth could one reasonably claim that Hamas is, in law, acting on behalf of the Palestinian people, and is thus exercising their right to self-defence? Hamas can call themselves the ‘resistance’ all they want, but there is only one internationally recognized representative of the Palestinian people, and that is the PLO.

This brings us to (3). Even if we accepted all of the propositions above as correct (and they are not), even if Hamas could somehow notionally be said to be defending the Palestinian people/Palestine, this does not entail that the 7 October action was an act of self-defence. Dr Wilde’s argument is that in bello illegality, i.e. the fact that Hamas forces killed and brutalized civilians on 7 October, does not ipso facto change the qualification of Hamas’ actions as ad bellum self-defence. He then offers us a couple of examples to support this claim, including one relating to Russia and Ukraine:

Imagine, hypothetically, that Ukrainian resistance fighters launched attacks within Russia involving targeting civilians, indiscriminate attacks risking harm to civilians, and the taking of civilian hostages. These attacks would be illegal, but they would not mean that Russia would then be legally permitted to extend its illegal war in Ukraine, in order to neutralize the threat of further such attacks.

For what it’s worth, it’s true that, if we look at the long arc of a conflict, in bello violations alone do not necessarily mean that a state exercising its right to self-defence is no longer doing so. But that does not entail that in bello violations – or even acts that don’t constitute violations of IHL at all – can’t change the ad bellum character of a state’s military actions, depending, in particular, on the purpose with which they are conducted. Consider, again, Ukraine and Russia. Imagine if Ukraine’s counter-offensive was miraculously effective, and that Ukraine very quickly managed to liberate all Ukrainian territories (including Crimea) from Russia. Imagine if then the victorious Ukrainian army advanced on to Moscow, despite calls by Russia for a ceasefire and its abandonment of any territorial pretensions to Ukraine. There is no in bello violation here by Ukraine at all. That is not the relevant ad bellum question. The relevant ad bellum question is whether Ukraine’s continuing armed response against Russia, even after Russia’s total defeat, would comply with the necessity and proportionality criteria of self-defence. In the hypothetical I just gave, Ukraine’s response, which started as self-defence against Russia, would eventually become an armed attack against Russia, and yes, Russia would suddenly possess the legal right to defend itself.

So, the real question for the Hamas actions on 7 October is not whether they were in bello violations (that much is obvious). The real question is whether those actions remained within the confines of ad bellum necessity and proportionality. Even if one accepted arguendo that Hamas was acting on behalf of Palestine/the Palestinian people, in defence against a continuing armed attack by Israel, how could one possibly accept that Hamas’ actions on 7 October were compliant with the necessity and proportionality requirements of self-defence? The operation on 7 October not only killed far more Israeli civilians than soldiers, but the civilians were killed deliberately, rather than incidentally. The primary purpose of Hamas’ actions was not to repel the ongoing Israeli attack against Palestine/Palestinians (however exactly defined), but to brutalize Israeli civilians and to capture many of them as hostages. The atrocity on 7 October cannot be characterised as an exercise of ad bellum self-defence because it manifestly had a punitive purpose, and could not even conceivably satisfy the necessity and proportionality criteria of self-defence. Had Hamas confined itself to killing Israeli soldiers, with a few civilians killed incidentally or even deliberately as an exception from the overall character of the operation, this assessment could be different. But, again, atrocity was the whole point of the operation. If you wanted a domestic law analogue, if somebody shot at me on a street, and I fired back at them, that would be self-defence. But if I then went to their house and killed their children, this would not be self-defence. The point hardly needs explaining, one would have thought.

So, just like in the victorious Ukraine example above, self-defence would no longer be a feasible characterization (if it ever was) of what Hamas was doing. Self-defence with a predominantly punitive purpose and/or which fails ad bellum necessity and proportionality is no longer self-defence, but becomes an attack. Whether Israel would have the right to defend itself against this attack depends on the considerations I examined above, and also on its own compliance with necessity and proportionality, to which I now turn.


Necessity and proportionality are the two customary limits on the right to self-defence, which are not expressly mentioned in Article 51. We only get to these criteria if (1) Palestine already was a state, or it was accepted that Article 2(4) protects self-determination units and that Gaza is part of such a unit; (2) we accepted that self-defence was available in response to armed attacks by non-state actors such as Hamas, or that the conduct of Hamas was somehow attributable to Palestine; (3) we also accepted that nothing in the jus ad bellum turns on the issue of whether Gaza remains occupied by Israel as a matter of the jus in bello; (4) we also accepted that Hamas was not exercising an Article 51 right to self-defence when it conducted its operation on 7 October. If all of these conditions are met, Israel would be exercising its right to self-defence by using force against Hamas in Gaza, and necessity and proportionality would set the limits on such a use of force. An Israeli response to 7 October that exceeded necessity and proportionality would itself become an attack, again to the extent that jus ad bellum applies in the first place.

The basic problem here, however, is that there are at least three ways of thinking about ad bellum, self-defence proportionality – the best scholarly exploration of this issue remains Professor David Kretzmer’s seminal 2013 article in the EJIL. The first conception of proportionality is tit-for-tat – a response in self-defence is proportionate so long as it is broadly similar in scale and effects to the attack. On this approach Israel’s response to the 7 October attack would be clearly disproportionate, as it has killed more than eight times as many Palestinians as the number of Israelis who died on 7 October. But, while states have used some variant of tit-for-tat proportionality when it comes to low-scale attacks and responses, essentially to limit risk of further escalation, this type of proportionality has generally not found state support for anything resembling the scale of the 7 October attack.

The second type of proportionality is ends-means proportionality. This is simply the idea that a use of force in self-defence is justified only as a last resort, no more than is necessary to do so. The key problem here is in defining the permissible goal, i.e. what is necessary. The moment one accepts Israel’s contention that the only way it could be secure is to destroy the capability of Hamas to attack Israel, it becomes very difficult to argue that Israel has exceeded the bounds of necessity. Missile strikes by Hamas continue and the hostages remain in its custody despite all the military force that Israel has already used. Israel can therefore argue that its continuing campaign remains necessary, since its goals are yet to be achieved – compare this to the hypothetical example given above of Ukraine actually succeeding in kicking Russia out of its territory, which would mean that any further military action would no longer be necessary. Thus, it is only if Israel’s goal of removing Hamas from power in Gaza is per se regarded as impermissible – and I’m not sure on what basis it could be so regarded, especially with Hamas leaders vowing that they would repeat the 7 October attack if they could – that ends-means proportionality could do any useful work in limiting Israel’s actions.

The third conception of proportionality – which Kretzmer called ‘narrow’ proportionality, and could also be termed proportionality stricto sensu – is very different. It would require a defender to strike a balance between the (possible) benefit gained by using force and the (actual) harm caused by it. In this particular context, Israel would need to demonstrate that its military campaign in Gaza is saving more lives in the long run than the lives it is taking right now.

This is the kind of proportionality that we need, that could do the real work here. I agree in that regard entirely with Adil Haque’s perceptive post on Just Security – as I noted above, with every day that goes by it becomes more difficult for Israel to argue that it is speculatively saving more lives in the future than it is certainly taking in the present. Israel can take many other measures to reduce the risk of Hamas doing again anything remotely approaching 7 October, that would not have as their consequence the continuing devastation of Gaza. I also don’t see how this balancing exercise could treat the value of Palestinian lives any differently from that of Israeli lives; if anything, the value of a life taken now means more than the value of a life that is perhaps saved in the future. While I am open to hearing any contrary argument, I don’t see how ethically the continuing loss of civilian life in Gaza can be justified, even if that loss is incidental rather than deliberate.

Legally, however, the critical problem is that states (and scholars) have not unambiguously endorsed this third, balancing conception of proportionality in the law of self-defence. Many leading experts of the jus ad bellum deny that this type of proportionality, even if morally required, is also required legally (cf. Rule 72 of the Tallinn Manual 2.0, with the International Group of Experts not even noting the possibility that this type of proportionality is required). I certainly know what the law should be in this regard, but it is difficult to make the argument that the law already is where it should be.


Whether Israel has an Article 51 right to self-defence is a complicated question that does not allow for binary answers. All possible answers turn on various underlying assumptions:

  1. If Palestine is not already a state, and there is no other option of extending the Article 2(4) prohibition on the use of force to Gaza, then Israel does not have a right to self-defence. This does not mean that Israel cannot use force in Gaza at all, but that the jus ad bellum would impose no constraints on it. I have no idea whether this would be the official view of the Israeli government. On the one hand, it is the most permissive in the ad bellum sense and aligns with Israel’s views on the statehood of Palestine, but, on the other hand, it would require Israel not to use the language of self-defence.
  2. If Palestine already is a state, or the prohibition on the use of force is somehow otherwise engaged, then Israel would have the right to self-defence if it were accepted that non-state actors such as Hamas are capable of committing armed attacks in the sense of Article 51 of the Charter, and that the operation on 7 October was one such attack. However, states and scholars remain divided on the core question of principle, although there has certainly been a growing trend of recognizing that non-state actors can commit armed attacks. Alternatively, Israel could even under a restrictivist view have the right to self-defence if the actions of Hamas were attributable to the state of Palestine, but any such attribution would be difficult.
  3. If the prohibition on the use of force was engaged, and Israel did not have the right to self-defence because none of the options in (2) was operable, then Israel could take no military action in Gaza whatsoever, no matter how limited, not even for the purpose of rescuing the hostages.
  4. If Israel did have the right to self-defence because one of the options in (2) was operable, its response would be limited by the necessity and proportionality criteria of customary international law. However, how precisely proportionality operates in these circumstances is highly contested, and Israel certainly has a plausible way of arguing that its actions remain proportionate, regardless of the number of Gazan civilians killed.

The combined effect of all of this uncertainty is such, in my view, that the jus ad bellum is of very little practical use with regard to the war in Gaza. Put differently, this is one of those cases in which the law runs out (leaving IHL aside for the moment, whose importance remains crucial, but which is structurally biased in favour of military necessity). This is one of those cases in which lawyers should not overly emphasise the law’s relevance or importance. This is one of those cases in which, in my view, ethics provides a clearer answer than the law. Morally, Israel can only justify taking the lives of innocents by saying that doing so would save more lives in the future. And the burden is on Israel to show that, even if it is not killing civilians intentionally, it is somehow still acting in such a way that will save more lives in the long run. This is not a burden that, in my judgment at least, Israel has so far met or is likely to meet. When confronted with this moral question, whether Israel has the right to self-defence under Article 51 of the Charter is largely beside the point.

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Ori Pomson says

November 14, 2023

Thank you, Marko, for this post.
Regarding whether the inapplicability of Article 2(4) is the official position of Israel, while I have not seen statements either way since October this year, it was at least Israel's official position in 2015 (at paragraph 67, footnote 97):
I would not go as far as arguing that this position "would require Israel not to use the language of self-defence", since lawyers generally raise alternative arguments in case the premise of their initial arguments are not accepted.

Martin Holterman says

November 14, 2023

Thank you for this thoughtful post. I have many questions, but I will limit myself to one:

What is the relevance of the fact that there is no peace treaty between Israel and the Palestinians?

As I understand it, a state of war has existed in Gaza and Israel since at least 1967. There may have been a cease fire, and there may be a peace treaty between Israel and Egypt, but neither ended the state of war in the Palestinian territories. Indeed, as I understand it, such a state of war is sine qua non for ongoing occupation.

On this basis, I would have thought that the question of art. 51 only arises with respect to Israel's original self-defence, which may well be in 1947, or otherwise the Six Day War or the Yom Kippur War. Or do the same ius ad bellum rules apply when hostilities are resumed following a cease fire?

Marco Longobardo says

November 14, 2023

Thanks, Marko.

It may interest readers to know that I have addressed these issues in detail in my monograph on The Use of Armed Force in Occupied Territory (Cambridge University Press 2018) pp. 88-133:

All the best,


André de Hoogh says

November 14, 2023

Dear Marko,

You say that article 2(4) of the Charter applies only to States, but this is not altogether clear. The first part of the sentence does speak of force against States (which therefore includes third States), but the second part can be divorced from the first part. In other words, Members shall in their international relations refrain from the threat or use of force ... in any other manner inconsistent with the Purposes of the United Nations. Now one of the purposes is to promote respect for the principle of self-determination of peoples. The qualifier 'international relations' can therefore be read to include the relation between a State and a people. If so, the continued military occupation (West Bank) and blockade (Gaza) by Israel would become relevant to the line(s) of reasoning concerning the right to self-defence as an exception.

Best wishes,

Nicolas Boeglin says

November 14, 2023

Dear Professor Milanovic

Thank you for this very good article. I would just like to point out that a word that Israel has repeatedly used in each of its official interventions and declarations to justify its military actions since 7 October (namely "terrorism", "terrorists") does not appear in your article.

It seems to me that as an Occupying Power, Israel cannot in any way claim a right to self-defence as enshrined in the United Nations Charter. And if we are to fight terrorism effectively, the so-called "war on terror" declared as such by the United States after 11 September 2001 is anything except a solution to the problem.

Finally, with regard to the intentionally killing of civilian by Israel, may I refer you (and our colleages at EJIL Talk) to this document containing stabbing testimonies of Israeli soldiers who took part in the 2014 ground offensive.

Looking at the figures for Palestinian deaths and injuries in Gaza since October 7th, 2023 it seems to me that the same type of instruction is given to the Israeli military. By the way, if you or our colleagues know of a similar document on testimonies of pilots and commanders of IDF aereal forces, please feel free to send me the link.

Sincerely yours

Nicolas Boeglin

Marty Lederman says

November 14, 2023

Thanks so much for this excellent post, Marko. I actually think you sell yourself short--that you provide the best answers to Questions 2 through 5, and demonstrate why the ad bellum question is not "a mess." (The fact that a handful of commentators and states differ does not a "mess" make.)

Most importantly, perhaps, you identify at the end the most important outstanding question, which is whether the Israeli operation as a whole can possibly satisfy *moral* requirements of proportionality.

That leaves the first question (is the Charter even implicated?). You're right that the answer is unclear--but does it matter? Wholly apart from the Charter, isn't it fair to say that there's a *customary* requirement of ad bellum proportionality? (I'd been assuming so, but perhaps that's mistaken.). More importantly: Does Israel or any other state even argue that it's permitted to engage in a *disproportionate* campaign to deter future attacks from an organized armed group?

José Alves says

November 14, 2023

Excellent post, Marko. Makes me think about the whole discussion whether self-defence is an exception to the use of force (and therefore needs to be interpreted restrictively) or an inherent "right" of states. Also, there is a superb post by Dapo some years back on the same issue.

Also, I'm impressed about how people use the comment section to advertise their own "work", even though we are discussing an extremely serious situation...

Brian L. Cox says

November 14, 2023

Thank you, Marko, for sharing this incredibly insightful and reflective article. Making a conscious, deliberate effort to engage not only with the substance presented in scholarly discourse but the personal motivations and beliefs *behind* the work truly is an invaluable pursuit in public discourse. Not only does doing so permit a richer and more productive exchange of ideas, but it also helps defuse the divisive and polarizing rhetoric that exists in public discourse in general and, increasingly, in the context of scholarly discourse.

I submit this comment without sharing my views on the substantive ad bellum points raised by Marko in the article. There will be plenty of opportunities and venues to do so in future. For purposes of this comment, I simply want to express my admiration and appreciation related to Marko's reflections on the topics of purpose and perspective raised above. This article will now be assigned reading when I get back to teaching international law and the use of force - not in the ad bellum blocks of instruction (although it would of course offer a splendid contribution there as well), but in support of discussions exploring the effect of and importance of motivation and perspective underlying the works with which we engage in class. Thanks again, Marko - nicely done (as always!!).

Juna Icaza says

November 14, 2023

It is great to see a post pointing to this crucial point which many people seem to overlook: The fact that Art. 51 UNC may not apply, since it is an exception to Art. 2(4) and 2(4) is most likely not violated. As soon as "non-state" entity is mentioned, most peoples' attention seems to directly shift to Art. 51 and the question of non-state actors thereunder. Thank you, Professor Milanovic, for this excellent post and your precise explanation of the legal issues!

Marko Milanovic says

November 15, 2023

Many thanks to everyone for the comments. Apologies for applying belatedly and only briefly, I'm travelling long-haul.

Ori, thanks a lot for that reference. It's very interesting to see how the Art 2(4)-not-engaged argument is relegated to a footnote. The law aside, the rhetorical power of self-defence is such that it's no wonder that Israel would want to rely on the concept, while hedging on the formal legal front.

Martin, as far as I'm concerned nothing at all depends on whether there's a pre-existing armed conflict between Israel and Hamas, or Israel and the state of Palestine. Arguments have been made in the literature that the jus ad bellum is relevant only at the initial point force is used, a theory that would relegate it to nothing in the case of a long-standing conflict such as the Israeli/Palestinian one. I don't think that reflects state practice. The existence of a formal state of 'war', to whatever extent it even applies today, is even less relevant. There is no peace treaty between North Korea and the US and South Korea etc, but any resumption of hostilities between these states would have to comply with the jus ad bellum.

Andre, the argument you've made about the scope of 2(4) has also been discussed in the comments to my 2009 post and Dapo's 2014, cited in my post above. Maybe that argument is plausible to some extent, but it's far from obvious and is not supported by the drafting history of 2(4) nor by any other unambiguous authority. There's a steep road to climb in arguing that some special type of non-state actor is covered by 2(4), that's all I'm saying.

Marko Milanovic says

November 15, 2023


The notion of 'terrorism', however defined, is essentially irrelevant from a jus ad bellum standpoint. Nothing depends on whether Hamas is qualified as a terrorist entity or not.

As for the argument that self-defence does not apply in occupied territory, I've addressed it in my post above. Again I think it's important to distinguish between at least two such scenarios, as I've explained. I don't think para 139 of the Wall AO really suggests otherwise. But the basic point is this - even on the assumption that self-defence somehow doesn't apply to hostilities in or emanating from an occupied territory, that does NOT entail that the occupying power is not allowed to use force in the occupied territory or is confined to 'law enforcement' measures only. When the US/UK were faced with an insurgency in Iraq, they were not prohibited to use force to fight that insurgency as a matter of the jus ad bellum.

Marko Milanovic says

November 15, 2023


Israel has not argued that it is not constrained by any notion of proportionality in fighting Hamas. Of course they haven't - it would sound completely horrible politically if they did so. But they haven't said they are subject to some specific version of ad bellum proportionality either, nor that proportionality (in the ad bellum sense) is some kind of independent rule. And as I explained there are at least three different approaches to what proportionality could be. Bottom line - Israel can certainly argue that its actions are compliant with SOME version of proportionality, e.g. ends-means, and it's difficult to argue that, as a matter of law, that version of proportionality is not the right one.

Eugenio Carli says

November 15, 2023

Dear Professor Milanovic,
I do not need to dwell on the quality of your post - the tenor of the comments you have received speak for themselves. Thanks for sharing that.
I just want to say a couple of things.

First, a personal opinion. Referring to your conclusion, I am not fully persuaded by point 1 since I do not think Article 51 is to read in such a close conjunction with Article 2(4) as you put forward. As I see it, the facts, among others, that an ‘armed attack’ under Article 51 does not perfectly equate to the use of force under Article 2(4) (though of course an ‘armed attack’ does also constitute a violation of article 2(4)) and that self-defence as being (one of the) exception(s) to prohibition of use of force is not as such made explicit in the Charter but is (please pass the words) a “scholarly construction”, perhaps prove that the two provisions are to be read separately. Consequently, I think that your second point ought be severed from point 1 and that it sort of assists my doubt: if self-defence against non-state actors is at stake, that is so (or should be so) regardless of the fact that a state from where the attacks originate exists. This in turn makes me suppose that Israel has in principle a right to self-defence under international law even where Palestine is not a State.

Second, I praise and fully support your conclusion that “[...] this is one of those cases in which the law runs out […]. This is one of those cases in which lawyers should not overly emphasise the law’s relevance or importance. This is one of those cases in which, in my view, ethics provides a clearer answer than the law”. Allow me to quote the words of the distinguished Italian international lawyer Benedetto Conforti on this point from his famous textbook Diritto internazionale, which fully endorse your view: “quando la forza è usata su larga scala, quando si è in presenza di una vera e propria guerra internazionale o civile, e non di un episodio isolato di uso della forza, e d'altro canto il sistema di sicurezza collettiva dell'ONU non riesce a controllarla e a funzionare, c'è forse da prendere atto che il diritto internazionale […] ha esaurito la sua funzione. La guerra non può allora essere valutata giuridicamente ma solo politicamente e moralmente. Politicamente e moralmente essa può essere giustificata o condannata a seconda dei valori che persegue e del suo eventuale presentarsi come il male minore. Ma dal punto di vista giuridico, essa non è né lecita né illecita, è indifferente. Insomma è questo un caso che dimostra che un ordinamento giuridico può avere delle lacune e che non è vero che esista sempre una norma di chiusura dell'ordinamento, per cui tutto ciò che non è vietato è permesso”. Roughly translated: when force is used on a large scale, when there is a real international or civil conflict, and not an isolated episode of use of force, and on the other hand the UN collective security system fails to work, it is perhaps worth acknowledging that international law […] has exhausted its function. The war cannot then be evaluated legally but only politically and morally. Politically and morally it can be justified or condemned depending on the values it pursues and whether it presents itself as the lesser evil. But from a legal perspective, it is neither legal nor illegal, it is indifferent. In short, this is a case that demonstrates that a legal system can have gaps and that it is not true that there is always a closing rule for the system, whereby everything that is not prohibited is permitted.

Marty Lederman says

November 15, 2023

Thanks again, Marko. I've been assuming that Israel's view on ad bellum proportionality is reflected in paragraph 69 of its Report on the 2014 Gaza campaign--namely, the dominant (even if not universal view) that the proportionality condition prohibits force beyond that necessary to achieve the lawful objective (there, "to repel attacks and eliminate the continuing threat"):

"Israel’s use of force was also proportionate, given the need to repel the attacks and reduce the continuing threat posed by Hamas and other terrorist organisations operating out of the Gaza Strip. [citing Mike Schmitt and John Norton Moore, FWIW.]. Israel responded to rocket fire throughout the month of June 2014 and in early July 2014 with limited strikes using precision-guided munitions. However, when faced with an escalation of violence that culminated on July 7 with more than 60 rockets fired at Israel in a single day, the Government of Israel was compelled to expand its use of force. Hamas’s continuation of rocket and mortar fire against Israel throughout the 2014 Gaza Conflict demonstrated the need for Israel’s sustained military action. In this context it should be stressed that the number of civilian
casualties of the adversary in the context of a military operation does not necessarily suggest that
military action was disproportionate. Rather, under the Law of Armed Conflict, the
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."

Marko Milanovic says

November 15, 2023

Hi Marty, yes, that's clearly self-defence proportionality, and the ends-means (no more than necessary) version thereof. It's not some kind of standalone proportionality principle.

Asher Rottenberg says

November 17, 2023

There might be reason to doubt that Hamas holds no obligation to the prohibition on the use of force as a matter of customary law. While this topic has been addressed in existing literature, it remains important to voice concerns whenever the assertion is reiterated.
Regarding the comparison between Israel’s strike in Gaza without Palestine’s consent and Israel's strike on Hizballah without Lebanon’s consent, a distinction arises due to the Oslo Accords. These accords, assuming they are still in force and binding for Palestine (distinct from the PLO, the signatory to the Oslo Accords), may implicitly provide consent for Israel to intervene when Palestine is, at the very least, unable to ensure Israel is not attacked as required by the Oslo Accords. No such agreement exists between Israel and Lebanon.
Concerning strict proportionality, benefit should not be confined solely to human life. It should also encompass other potential humane benefits, such as living life without the fear of potential terror and fostering a prosperous atmosphere in both Gaza and Israel. Therefore, defining the benefit cannot solely rely on the number of lives but necessitates an evaluation of the overall situation today and potentially in the future. This evaluation is not straightforward and involves input from strategic and political scientists, historians, and military experts, making it presumptuous for lawyers to do so without such multidisciplinary collaboration. The challenge lies not just in the increasing death toll but in quantifying or describing the “benefit.” As long as a state can reasonably claim a benefit, demanding quantifiable measures becomes difficult.
Lastly, considering morality: while this isn’t the primary focus here, it’s worth noting that the simplistic utilitarian argument is inadequate and fails to consider certain aspects. First, Israel has a moral obligation to protect its national interests, which might necessitate reactions resulting in more Palestinian casualties (similar to the argument where a father must prioritize his own child over someone else's). Second, Israel claims that the killing of people in Gaza is often unintentional, at least according to their assertions, though the reality remains unclear.

Ed Damvelt says

November 17, 2023

It is unavoidable that, as society evolves, situations occur that never before have been pre-visioned in the inherent legal development. Laws are invariably made as a consequence after facts, never before for situations that are hitherto unknown and unforeseen.

If then comes a case like this, it is a futile exercise to try to apply existing laws to situations that they have not been provided for. It makes more sense to attend to the legal development as dictated necessary by this particular case.

Ruvi Ziegler says

November 23, 2023

Thanks Marko. You say in one of your responses that 'Israel can certainly argue that its actions are compliant with SOME version of proportionality, e.g. ends-means, and it's difficult to argue that, as a matter of law, that version of proportionality is not the right one.' I would then want to hear more about why, a a policy matter, for an international order in which states have the primary responsibility for maintaining the security of those residing in their territory (including their ability to reside their free of continuous external attacks), you express a preference for an alternative version which detrimentally affects their ability to do so.

Matthias Zechariah says

November 24, 2023

I agree with Damvelt's view, but with leaning towards the expansionist approach. Essentially, the issue in discourse was not pre-envisioned. Whereas scholarly exercise is healthy and necessary on the issue, we should not seek to find a determinate legal solution to what is clearly outside the extant normative domain. Morality and pragmatism (or politics?), as opposed to law, may be more at play in the Israeli-Hamas scenario. Perhaps, a rule of customary international law may soon evolve on this.

Nicolas Boeglin says

November 24, 2023

Dear Professor Milanovic

Thank you very much for answering my question.

Regarding the reaction of the US and the UK in Iraq when attacked by militias, I consider we cannot use this situation and compare it to what is happening in Israel, as these military groups or militias were attacking US and British military personnel in Iraq (and not the US or British civilian population).

It is quite striking that Israel's unique legal argument to justify its collective punitive operation in Gaza ("fighting terrorism" and "erradicating Hamas terrorists") has no place in the rules that apply to international conflicts.

If I´m not wrong, after 11/S, Israel adopted a legislation very similar to that of the United States on "unlawful combatants" in its fight against "palestinian terrorism", precisely in an attempt to circumvent international rules on the matter. If any colleagues have knowledge of this Israeli legislation, thank you for sharing it.

Yours sincerely

Nicolas Boeglin

Note: with regard to last OCHA - OPT report (to November 23), we read in it that:

"According to the Government Media Office (GMO), as of 18:00 on 23 November, more than 14,800 people have been killed in Gaza, including about 6,000 children and 4,000 women. This office, which is under the local authorities in Gaza, has assumed MoH’s role following the collapse of services and communications at hospitals in the north".