Self-Defense and Non-State Actors: Indeterminacy and the Jus ad Bellum

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Self-defense in response to armed attacks by non-state actors is undoubtedly one of the most interesting – and controversial – issues in modern international law. It is of great practical relevance, as for instance, with the ongoing use of drones for the targeted killings of suspected terrorists (a question I’ve discussed here), and has attracted a great deal of scholarly attention. Lindsay Moir has just published a book with Hart/Oxford that I’m sure will provide a strong contribution to the field. I would particularly like to draw our readers’ attention to the recent discussion in the EJIL provoked by Christian Tams’ excellent article on the use of force against terrorists, with responses by Federico Sperotto and Kimberley Trapp, and a rejoinder by Christian.

In this post, I would like to add a few thoughts on how the indeterminacy of state practice and opinio juris has caused an indeterminacy in the law, which I don’t think can be denied or removed by any legal analysis, no matter how exhaustive and competent.

Consider, first, that we are (I think) in broad agreement that the prohibition on the use of force in international law, as set out in Article 2(4) of the UN Charter, operates exclusively between states. If, instead of from Afghanistan, Al-Qaeda operated from and launched the 9/11 attacks against the United States from Antarctica, the high seas or some Dr. Evil-style terra nullius volcanic rock in the middle of nowhere (or the Moon even), the jus ad bellum would not in any way limit the US response to the armed attack. It is only if in responding to the attack the US has to encroach on the sovereignty of some other state that Article 2(4) is engaged. (See, similarly, our discussion regarding Israel’s intervention in Gaza). Of course, that in such a situation the jus ad bellum would be inapplicable does not mean that the use of force might not be regulated by some other body of law, such as humanitarian law or human rights law – but that is for now beside the point.

Consequently, it is only if Article 2(4) is engaged that the Article 51 right of self-defence comes into play, since it is an exception to the prohibition on the use of inter-state force. Sure, one could generally say that in responding to an attack by a non-state actor which does not operate from the territory of another state the attacked state is acting in self-defence. But such a characterization would be merely descriptive – this would not be the Article 51 notion of self-defence, which is relevant only when the attacked state responds by violating the sovereignty of some other state. This was, I believe, the case with the Israel’s incursion into Gaza.

However, and this is a crucial point, that Article 51 operates as an exception to the ban on the use of inter-state force, does not logically and conceptually entail that the ‘armed attack’ within the meaning of Article 51 must be attributable to a state. Such a conclusion may follow from an examination of state practice, but it simply does not follow from the text of the Charter or from some broader legal principle, nor from the fact that Article 2(4) itself is inter-state in operation.

So, with this in mind let’s turn to the 9/11 attacks as the paradigmatic example of a non-state actor attacking one state while operating from the territory of another state. The international community has been practically unanimous that the US invasion of Afghanistan was a lawful exercise of self-defence, though some have expressed certain doubts as to the proportionality of the regime-toppling intervention. If the US invasion is accepted as lawful, as I think it must be, there are two, and only two, possible explanations for its lawfulness:

(1) Article 51 requires that the ‘armed attack’ be attributable to a state, thereby engaging its responsibility. Therefore, the 9/11 attacks must have been attributable to the state of Afghanistan. However, the general rules of attribution of acts of non-state actors to states, as articulated by the ILC in its Articles on State Responsibility and by the ICJ in the Nicaragua and Genocide cases, do not allow for a reasonable interpretation that would attribute the 9/11 attacks to Afghanistan, because they require proof that Afghanistan either (a) had complete control over Al-Qaeda, rendering it a de facto state organ; or (b) that Afghanistan had effective control over Al-Qaeda’s conduct in question, i.e. the 9/11 attacks. Since there is no proof of either – indeed, far from it – the 9/11 attacks cannot be attributed to Afghanistan under the general rules. But, because the US invasion was a lawful exercise of self-defence (so we all agree), the attacks MUST have been attributable to Afghanistan. Therefore, the general rules of attribution have either changed, or lex specialis rules of attribution have emerged, whether confined to ‘terrorist’ armed attacks or to the jus ad bellum more broadly, to allow for looser standard of attribution, such as harbouring terrorists or complicity in their actions.

(2) Article 51 does NOT require the attribution of the armed attack by a non-state actor to a state. Rather, for the attacked state to respond against the non-state actor which is operating in another state, the conduct of this latter state must be such to justify the ensuing violation of its sovereignty. Various authors have proposed different standards, but three scenarios seem generally possible, on a scale from the most to the least stringent: (a) the territorial state was complicit or was actively supporting the non-state actor in its armed attack; (b) the territorial state failed to exercise due diligence, i.e. it did not do all that it could reasonably have done to prevent the non-state actor from using its territory to mount an armed attack against another state, or is not doing all it can to prevent further attacks; (c) the territorial state may have exercised due diligence, but it was nonetheless unable to prevent the attack, or to prevent further attacks. The US post-9/11 invasion of Afghanistan could be quite comfortably justified under these standards.

One of these two options MUST be true if the US invasion was a lawful exercise of self-defense. No third option exists, as far as I can see. True, the two options may not lead to different ultimate results in the same factual situations. They are, however, conceptually significantly different and have other, broader implications. The first option couples the jus ad bellum and the law of state responsibility, while the second does not. If the first option is true, then the law of state responsibility must change whenever the jus ad bellum needs to accommodate a more lax standard of self-defense in response to armed attacks by non-state actors. And this is precisely what Christian argues in his initial EJIL piece – that a less stringent rule of attribution which is specific to the jus ad bellum context has evolved. Similarly, see Steve Ratner’s article in 96 AJIL 905 (2002).

Personally, I find the second option to be significantly more preferable to the first, because it maintains the distinction between primary and secondary rules that was famously introduced by the ILC project on state responsibility. That distinction serves several purposes. It helps us solidify general rules of state responsibility while avoiding politically sensitive questions, such as initially rules on treatment of aliens, or now self-defense against non-state actors. It relegates the discussion of these politically thorny questions to the body of primary rules that regulate them – here to the jus ad bellum. Thus, for instance, Kimberley has persuasively argued in her ICLQ article that it is the customary necessity condition for the lawfulness of self-defense that governs an attacked state’s response to an armed attack by a non-state actor operating from another state. We may disagree in precisely what circumstances on the (a) – (c) spectrum that I have outlined above such necessity would exist, but this is precisely the area where such debates should be had, instead of tinkering with the law of state responsibility. Finally, there is an inherent value in having general, coherent secondary rules of attribution which apply irrespective of the primary rules that are being applied, as this enhances the systemic character of international law, and helps it resist fragmentationist impulses.

In other words, it is as a general matter undesirable to have rules of attribution which are primary rule-dependent. Of course, that this is undesirable doesn’t mean it can’t happen. Article 55 of the ILC ASR expressly allows for secondary rules which are lex specialis. But the rules of attribution are precisely the core concept of the law of state responsibility, where lex specialis should not be accepted lightly. This is especially so because it is hard to justify in principle, say, why there should be special rules of attribution when it comes to the use of force by non-state actors pure and simple, but no such rules when it comes to how that force is used, e.g. in regard of genocide or crimes against humanity, as in the Bosnian Genocide case.

Be that as it may, my main point is this: even though I strongly prefer the second option, I still have to say that both options are on the table. For the time being at least, it is objectively impossible to tell which option is valid from an examination of state practice, opinio juris, and the case law. The ICJ has expressly reserved its position on whether Article 51 requires attribution of the armed attack to a state in Congo v. Uganda, despite its earlier pronouncements in Nicaragua and in the Wall case (the latter in my view being better explained by the fact that the armed attacks in question emanated from non-state actors operating from Israeli-occupied territory, thereby disengaging Article 2(4), and consequently Article 51). As for state practice, the official pronouncements of states in the relevant cases are far too ambiguous to say one way or the other whether states consider that Article 51 requires attribution, but that lex specialis rules of attribution have emerged, or instead that no attribution requirement exists.

Take for example the 2006 Lebanon war. Israel was attacked by Hezbollah, a non-state actor operating from within Lebanon. Israel responded by invading Lebanon, thereby engaging Article 2(4), and requiring a justification under Article 51. The reaction by states and other actors has generally been that Israel was entitled in principle to act in self-defense, but that its actions were disproportionate (e.g. because it did not exclusively target Hezbollah). But neither the Israeli official position on its use of force nor the international reaction to it were clear enough to conclusively decide between options (1) and (2).

For example, on 12 July 2006 Israeli Prime Minister Ehud Olmert made the following statement:

This morning, actions were carried out against IDF soldiers in the north. At this time, the security forces are operating in Lebanese territory. The cabinet will convene this evening in order to approve the continuation of the activity.

I want to make it clear: This morning’s events were not a terrorist attack, but the action of a sovereign state that attacked Israel for no reason and without provocation. The Lebanese government, of which Hizbullah is a member, is trying to undermine regional stability. Lebanon is responsible and Lebanon will bear the consequences of its actions.

Here we obviously have a claim by Israel that the armed attacks against it from Lebanese territory were attributable to Lebanon as a matter of state responsibility. But only a few days later, on 16 July 2006, after the Lebanese government denied that it was responsible for the attack, the Israeli position was different:

Prime Minister Olmert emphasized that Israel is not fighting Lebanon but the terrorist element there, led by Nasrallah and his cohorts, who have made Lebanon a hostage and created Syrian- and Iranian-sponsored terrorist enclaves of murder.

Here Lebanon was no longer the author of attacks and responsible for them, but the ‘hostage’ of a non-state actor. This to me sounds a lot like option (2), but there is nonetheless no way to say this with certainty. And the reactions by other states are even more ambiguous (see, e.g. the Security Council debates in S.PV/5489), though to me it seems that many states have accepted Israel’s claim to self-defense without saying that Lebanon was responsible for the attack.

In other words, not even the state using force, Israel, actually articulated a clear position either in favour of option (1) or option (2). Nor did for, that matter, the United States when it invaded Afghanistan. And when the states responding in self-defense refrain from articulating a clear position – probably because they believe that there is some benefit in the ambiguity – then the reactions by other states are almost by definition useless in choosing between the two options. Sure, these states might tell us whether they thought that the use of force was lawful, but they would not explain the theory on which they base their conclusion.

To me, therefore, the conceptual questions of self-defense against non-state actors remain utterly indeterminate while state practice remains as it is. We as lawyers may certainly choose between the two options, but we do so solely – solely – on policy grounds. There’s nothing wrong with that, mind you, and all of the reasons I’ve given above favouring option (2) are no more, and no less, than reasons of policy. And if this is so, there’s also nothing wrong in openly acknowledging the law’s indeterminacy.

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John C. Dehn says

February 22, 2010

Nice post, Marko, though I disagree that there are only two legally satisfactory explanations possible in these circumstances.

The Responsibility of States for Internationally Wrongful Acts (RSIWA) draft articles (adopted by the ILC, noticed by the General Assembly), include in the situations which preclude the wrongfulness of a breach of an international obligation:

Article 25: Necessity
1. Necessity may not be invoked by a State as a ground for precluding the wrongfulness of an act not in conformity with an international obligation of that State unless the act:
(a) Is the only way for the State to safeguard an essential interest against a grave and imminent peril; and
(b) Does not seriously impair an essential interest of the State or States towards which the obligation exists, or of the international community as a whole.

Your option #2, above, basically articulates a requirement for state responsibility, rather than attribution. In earlier posts here, I have argued with Jordan Paust that this might be the best way to view the problem. Host states would rarely meet option #1.

It may not be necessary to place the strained interpretation of Art. 51 that you suggest in your option #2. It would also seem possible that the above article describing necessity, if an accurate statement of customary international law, might excuse the violation of another state's sovereignty even without an invocation of that state's responsibility. Would you not agree? If not, why not?

Furthermore, on what theory would you say that your #2 option "justifies" a violation of sovereignty. I ask because, assuming you are correct, the RSIWA provide only two "justifications" precluding wrongfulness: self defense and countermeasures (the rest, such as necessity and distress, are more properly termed "excuses").

Self defense does not apply without attribution, as you noted, unless we are to reinterpret it, as you appear suggest. Resort to countermeasures carries many requirements for its exercise (such as notice of intent to resort to countermeasures) that may not be met under the circumstances of many of these attacks.

Is it not better to see these situations as proof of the customary status of Article 25 (with perhaps a broader understanding of "grave and imminent peril") rather than suggest a new customary gloss on Article 51?

Mihai Martoiu Ticu says

February 22, 2010

What about self-defense of the non-state actors against states attacking them? Imagine that you are a tribe attacked by drones and you want to defend yourself. Could you target kill Obama or someone?

Marko Milanovic says

February 22, 2010


(i) I don't think it strained at all to interpret Article 51 as not requiring attribution of the armed attack to a state. All it says is that self-defense applies 'if an armed attack occurs against a Member of the United Nations.' It simply doesn't say that the armed attack must be by another state. As I argue above, this conclusion may nonetheless result from state practice etc, but it is not textually warranted.

(ii) As for necessity as a circumstance precluding wrongfulness under Art. 25 ASR, states using force against terrorists are simply not relying on it - rather, they are invoking self-defense, and the only justification that counts is the one that the state itself offers, per Nicaragua. As a matter of principle, I don't think that necessity alone can be used to justify the use of force in violation of the sovereignty of another state, since it by definition impairs the essential interests of the other state. Nor does, for that matter, the ILC:

"As embodied in article 25, the plea of necessity is not intended to cover conduct which is in principle regulated by the primary obligations. This has a particular importance in relation to the rules relating to the use of force in international relations and to the question of “military necessity”. It is true that in a few cases, the plea of necessity has been invoked to excuse military action abroad, in particular in the context of claims to humanitarian intervention. The question whether measures of forcible humanitarian intervention, not sanctioned pursuant to Chapters VII or VIII of the Charter of the United Nations, may be lawful under modern
international law is not covered by article 25. The same thing is true of the doctrine of “military necessity” which is, in the first place, the underlying criterion for a series of substantive rules of the law of war and neutrality, as well as being included in terms in a number of treaty provisions in the field of international humanitarian law. In both respects, while considerations akin to those underlying article 25 may have a role, they are taken into account in the context of the formulation and interpretation of the primary obligations."

In short, what the ILC quite sensibly says is that the use of force is completely regulated by applicable primary rules, which exclude a reference to secondary rules on circumstances precluding wrongfulness (not to mention the fact that the rules on the use of force are widely considered to be jus cogens - see Art 26 ASR and commentary). And the primary rules, the jus ad bellum, do not allow for a use of force merely because it is 'necessary' - or considered by a state to be necessary. Necessity is of course taken into account with regard to self-defense, but it presumes the existence of an armed attack.

(iii) My reference to a justification for the violation of the sovereignty of a state from whose territory a non-state actor initiates an armed attack is not one to a circumstance precluding wrongfulness, but to the content of the applicable primary rule. It is Article 51 and customary law which could be interpreted more or less broadly with regard to what exactly the state needs to have done (if anything - see option (2)(c) above: mere inability to prevent attacks may suffice) in order for the attacked state to be able to respond lawfully.


Non-state actors have no right to self-defense against attacks by states simply because they do not need it. It is in principle not unlawful in international law for non-state actors to attack states - just like Art 2(4) does not prohibit states from attacking non-state actors. Depending on the circumstances, of course, international criminal law may come into the picture, as would domestic law, with entirely different notions of self-defense.

Mihai Martoiu Ticu says

February 22, 2010


Imagine that you are the mother of a 4 year old daughter watching her playing in the garden. Suddenly she explodes. You look upwards and see a drone with stars and stripes. Imagine that you think that this is not OK. To what judge you can go? Or are you allowed to do the same thing to Obama? Or just tell me what’s the next step you can take.

Jonathan Ketcheson says

February 22, 2010

Dear Marko,

You make many interesting points and have certainly made me think about this issue in a new light. However, my personal view is that one needs to abandon the position that the events of September 11 can be reconciled with the current state of international law, at least if you take the position that international law is what the ICJ says it is.

There were other bases for the decision in the Wall opinion that would have avoided the Court making the statement that an armed attack needed to be by a State (eg. as you say, article 51 was simply not engaged/relevant). But I don’t think there is any way of avoiding that this is what the Court said. The opinion of Judge Higgins is illuminating in these respects. You are right that DRC v Uganda avoided this issue. One can probably say no more than that it is consistent with the Wall/Nicaragua but I understood the reason for this (and the absence of any dissents) to be that the relevant events in that case took place pre-September 11.

I agree with your option 2 as a policy choice. The problem with it being that the ICJ had a “hook” in the form of “sending” (Definition of Aggression) but seems to have treated this as being equivalent to attribution, seemingly excluding any middle ground. The Court is less than explicit in DRC v Uganda but I read (see para 160) the judgment as affirming that the general rules on attribution (with the possible exception of retrospective attribution eg. Article 11 DARSIWA) as applying in determining whether or not an armed attack was by a State (ie. excluding your option 1 as an explanation of the lawfulness of September 11). However, I am sure that the ICJ has enough “magic tricks” to get itself out of the mess it has created if it wished.

You are right that the law remains indeterminate. Absent any judgment or prospect of judgment by the ICJ, States have enough material and lack of certainty in the law to be able to argue any number of positions. The law on the jus ad bellum (not just with respect to the non-State actors issue), as outlined by the ICJ, is open to the “critique of utopia”. One can understand why the ICJ would want to limit recourse to the use of force but the law enunciated by it simply cannot be reconciled with realities/practicalities. I think that the opinion of Sir Robert Jennings in Nicaragua was in many respects prescient.

I should confess that I haven’t really kept on top of these issues post DRC v Uganda. But I still subscribe to my main point: you cannot reconcile the lawfulness of September 11 and the jurisprudence of the ICJ.

John C. Dehn says

February 22, 2010


I think you might be reading the ILC's necessity analysis too broadly, in this context. Reasonable minds can certainly differ.

Necessity cannot be used to directly attack a state or seize its territory in violation of Arts. 2(4) and 51. Article 2(4) indeed states an essential interest of a state if the attack is "against" its political independence or territorial integrity. Likewise, necessity cannot be used to justify a violation of the jus in bello. This is as much as the ILC says about the limits of necessity, in my opinion, and does not preclude its use in this context.

I am not sure whether necessity can be used to justify an infrigement of sovereignty necessary to exercise the right of self defense against a non-state actor. There are two operative principles: self defense operable against the non-state actor; and necessity (or responsibility coupled with countermeasures) operable with regard to the territorial sovereignty of the host state. I am in the class of individuals that believes these attacks do not necessarily implicate Art. 2(4) unless the host state is itself attacked. A more interesting and problematic analysis would be required for, say, the invasion and occupation of the FATA in Pakistan.

There is no necessary inconsistency with a state's invoking self defense against a non-state actor to justify an attack, and a resort to a necessity (or countermeasures) analysis in order to infringe the sovereignty of another state in doing so. For me, it is problematic to extend the concept of self defense beyond the entity against which force is used. It seems that one must necessarily must invoke a justification or excuse operable on the right being infringed, in this case the territorial sovereignty of the host state.

It may be appropriate then, to look to the concept of necessity in a normative assessment of these states' claims. In your option #2, the host state's actions or inaction might justify a resort to countermeasures, or may indicate the lack of an "essential interest" in the host state, or may simply indicate the lack of alternatives justifying the resort to self defense coupled with a necessity analysis.

I'd be interested in your thoughts on these comments. Of course, if you believe Art. 2(4) is implicated in each of these attacks, I understand why you would find a necessity analysis problematic in this context.

Marko Milanovic says

February 22, 2010


With regard to your US example, the only courts which the individuals concerned would petition are US domestic courts, since the US has not accepted the jurisdiction of any international human rights tribunal. If it were a European country that did the killing, the victims could conceivably petition the European Court of Human Rights. Both alternatives require an examination of the extraterritorial scope of domestic or international human rights protection, and with the case law as it is, both would have low prospects of success.


Agreed, but for two points:

While I think it would be fair to say that the ICJ jurisprudence is at odds with post-9/11 developments (though, again, it is in my view a bit more ambiguous), I certainly don't subscribe to the view that the law is what the ICJ says it is - particularly when substantive reasoning is lacking. The ICJ can be wrong on something just like any other court.

Also, as for Congo v. Uganda, the Court didn't leave the issue open necessarily because the events took place before 9/11. Rather, the facts of the case were such that they did not have to involve themselves with the whole question of self-defense of non-state actors, and a majority of the Court didn't want to touch the issue with a stick. Judges Kooijmans and Simma were less cautious, as you know. This is a frequent split between those judges who just want to solve the narrow dispute at hand, and those who want to provide more guidance for the future. To my mind, what the majority did was precisely to signal (contra Nicaragua and Wall) that they thought that the issue was still open - and see what happens in the future.


For my part, I am most emphatically in the camp which argues that Art 2(4) applies regardless of the motive of the state using force against another. Any invasion of Afghanistan by the US post-9/11 would have engaged 2(4) and justified within the jus ad bellum framework, even had the US limited itself strictly to Al-Qaeda and didn't even touch the Taliban. Any use of force in a state's territory without its consent engages the prohibition on the use of force. Making Art 2(4) dependent on state motive is not only contrary to the travaux and relevant practice (and, for what it's worth, a strong majority of academic opinion), it is an open invitation to abuse.

Mihai Martoiu Ticu says

February 22, 2010


You mean that our mother can actually ask an American judge to order Obama to stop the drone attacks, or find him guilty of any crime? Or that an Iraqi mother could have ask the judge to stop the invasion during the first days when it started?

Marko Milanovic says

February 22, 2010


To be blunt, I'm saying they could try, but that they would lose - either on grounds of jusiticiability/political question/separation of powers, or because the courts would say that the US Constitution does not apply extraterritorially. There is, however, quite a bit of litigation under the European Convention on Human Rights in the UK for the acts of its troops in Iraq - see, e.g., Al-Skeini, Al-Saadoon, Al-Jedda, with more or less success for the plaintiffs.

However, even under the ECHR, a drone attack would not be considered as falling within the territorial scope of the Convention (absent something more, such as belligerent occupation of the territory where the act takes place), per the European Court's (in my view wrongly decided) admissibility decision in Bankovic v. Belgium. Please do Google some of these cases if you need more background.

John C. Dehn says

February 22, 2010

Marko, while I agree with you in regards to a large physical ground invasion by armed forces, or an attack against the host state itself, I am uncertain I can agree with this statement:

"Any use of force in a state’s territory without its consent engages the prohibition on the use of force. Making Art 2(4) dependent on state motive is not only contrary to the travaux and relevant practice (and, for what it’s worth, a strong majority of academic opinion), it is an open invitation to abuse."

Are you so certain this aspect of your statement reflects "relevant practice"? Have you completed or are you aware of empirical analysis on this point? I do believe physical invasion and stand-off attacks without invasion are and have been treated differently by the international community (meaning how states and the U.N. respond to such events). State practice with regard to stand-off attacks against non-state actors pre-date 9/11 to be sure.

Why do you think it preferable to reinterpret Article 51, as you offer above, rather than Article 2(4) in light of this state practice? You are offering an interpretation that the text will support, as am I in regard to 2(4). It seems unnecessary to presuppose one is better than the other, or MORE susceptible of abuse. Both approaches might be abused, just as the Art. 51 "inherent" right of self defense has been interpreted by many to encompass more than responsive or imminent attacks.

I am offering a different possible normative description of state practice that is no more or less radical than those you summarize above, and which attempts to account for state practice pre-dating 9/11. As for what states offer in the ICJ or elsewhere, they will offer whatever justification they can. Self defense is easy, offers a politically solid sound bite, and is perhaps oversimplified from a doctrinal perspective. A different normative description might be preferable.

I can think of very good reasons it might be preferable to delimit 2(4) to a fair reading of its text ("against the territorial integrity" not "within the territory") and require a different justification or excuse for the violation of host state territorial sovereignty when attacking a resident non-state actor. In the final analysis, it might be better, worse or no different than your proposal to extend the concept of self defense to encompass the abrogation of an international obligation beyond its immediate object.

For me, the approach you describe is doctrinally unsatisfying absent a further legal principle directly operative upon the violation of the host state's territorial integrity. Otherwise, I am uncertain what "the conduct of [a host] state must be such to justify the ensuing violation of its sovereignty" means. What is the legal doctrine "justify[-ing]" this violation? Without a doctrine, one cannot define its limits. Perhaps this is why writers have been so free to suggest any reason they find personally satisfactory, and then shoehorn it into Article 51 "self defense".

Marko Milanovic says

February 22, 2010


Two points:

(1) I think it is inherently - yes, inherently - less open to abuse to set a broad prohibition, and then argue about the limits of a few narrow exceptions, than it is to undermine the prohibition itself. In any event, this is a very old debate - for both doctrinal and empirical analysis and arguments, I have nothing to add to the works of Brownlie, Christine Gray, Simma's Charter commentary, or Yoram Dinstein - see, e.g, Dinstein's War, Aggression and Self-Defense, at 91 ff. Whether you're persuaded by this international law orthodoxy is of course up to you.

(2) A more fundamental methodological point: as I have said above, the only justification of the use of force that matters is the one that the state itself officially professes. It is not for academics, nor for courts, to second-guess the political and legal judgment that this state has made, or be its psychoanalysts. It is for it to choose the 'normative description' from which it wants to argue its case.

Thus, for example, the only justification that matters for assessing the lawfulness of the second Iraq war is implied UNSC authorization or the so-called revival argument, not pre-emptive self-defense, humanitarian intervention or what have you, because this is the justification on which the states using force actually relied, and this is the justification to which other states reacted, all of them thereby expressing their opinio juris. See more D. Kritsiotis, 'Arguments of Mass Confusion,' (2004) 15 EJIL 233. This is an important lesson to draw from the ICJ's Nicaragua judgment - but again, whether your find it persuasive is up to you.

John C. Dehn says

February 23, 2010


Of course, I will once again put aside the tenor of your comments and simply say that it is no more or less orthodox to demand that doctrinal analysis or description in legal commentary comply with observed international practice and certain well-settled legal principles than it is to assert preferred legal arguments and understandings based on treaty text and travaux. It seems a bit hypocritical to take certain treaty terms as "settled" or "old debate" and assert a normative evolution in others. A balanced analysis would seem to require consideration of all possible developments/explanations for what we observe. This is all I am suggesting, as I have not argued for one or another view of the law. (As for "empirical analysis," we must be using different definitions given the authors you cite. I am very familiar with their principle works and would describe them as qualitative, not empirical.)

I do take your point regarding what states claim, when they claim anything at all. My point was that "self defense" alone might be an incomplete doctrinal description of the phenomena we are witnessing. It is not psychoanalysis to look behind the substance of a claim and piece together its necessary elements, whether expressed or not. If states find it necessary to assert "responsibility" of a host state in this context, as might be the case and some authors believe is needed, that has implicit normative implications that might be better described in terms other than self defense.

Of course, Nicaragua might just be wrong, as you say, and "responsibility" rather than attribution may be enough to justify a 2(4) violation so long as the attack seeks only to eliminate a threat on a host state's territory, with the degree of host state responsibility and the principle of proportionality regulating the magnitude of 2(4) violation justified. The risk of abuse in this "narrow exception" would seem to be obvious. Was invasion of Afghanistan and deposing the Taliban regime justified or proportionate to the al Qaeda attack and on-going threat? Reasonable minds might certainly differ.

By the way, to invoke a state's responsibility and resort to the concept of countermeasures to justify a breach of territorial integrity, if that is one way to view this problem, does not require a rethinking of 2(4). Only a necessity claim potentially requires that, assuming of course an essential interest is implicated by the use of force within, rather than against, the host state.

At the end of the day I do believe this. If a person presents a threat to me, I can proportionately respond to it under the criminal law of developed legal systems. The right to do so does not, of itself, permit me to infringe the rights of a bystander. Even if I claim that I was acting in self defense, the court will require more. A different legal principle is necessary to excuse or justify that infringement. That is all I seek in this context, with an open mind.

Mihai Martoiu Ticu says

February 23, 2010


From your reaction we could conclude that our Pakistani/Iraqi mother could neither go to an international court, nor to an American one. That means that law is totally unusefull for them in such a case?

jpaust says

February 23, 2010

At least two false premises have arisen: (1) "it is only if Articl 2(4) is engaged that Article 51 ... comes into play," and (2) use of force on foreign state territory necessarily "violates" the "sovereignty" of that state. Each begs the very questions at stake. As noted in my draft article, 2(4) is limited to certain (not all) uses of force by a "state," but 51 does not use the word "state" and recognizes the "inherent" right of self-defense in case of an armed attack. Clearly, the "inherent" right of self-defense includes what had been recognized during and since The Caroline case as a right of self-defense against non-state actor attacks even when there was, in modern parlance, no state attribution or a violation of 2(4) by a state from which the non-state actor attacks emanate. Secondly, sovereignty is limited by international law, especially the legal right of self-defense. Members of the U.N. have even "consented" to use of the "inherent" right of self-defense in case of an armed attack when ratifying or aceeding to the U.N. Charter and its Article 51.
JJ Paust

Marko Milanovic says

February 23, 2010

Prof. Paust,

As for your point (1), I honestly can't see how you can argue that Art. 51 has a meaningful existence independent of the prohibition on the use of force. Sure, it's 'inherent', but prior to the use of force being prohibited by the Kellog-Briand Pact and then the Charter there was no use for self-defence other than perhaps as a facet of necessity as a circumstance precluding wrongfulness, if I can be forgiven for using these terms somewhat anachronistically. Who needs self-defence to justify using force when using force itself is not prohibited anyway?

To my mind, Art. 51 clearly stands as an exception to Art. 2(4). As I've said above, if a non-state actor launched a missile at a state from Antarctica or from a pirate ship on the high seas, the attacked state simply does not need to justify its use of force against that non-state actor, because the use of force is not prohibited unless it infringes on another state. In that sense Art. 51 is not engaged if Art. 2(4) is not - please provide an example to the contrary if you have one. The Caroline certainly is not one, as the UK/Canada responded to an attack coming from US soil. In modern parlance, Art. 2(4) would have been engaged.

As for the relevance of Caroline, please see ILC ASR Commentary, p. 196, para. 5: "The “Caroline” incident of 1837, though frequently referred to as an instance of self-defence, really involved the plea of necessity at a time when the law concerning the use of force had a quite different basis than it now has."

Likewise, see ILC commentary to Art. 21 ASR, at 177-178:

“The existence of a general principle admitting self-defence as an exception to the prohibition against the use of force in international relations is undisputed. Article 51 of the Charter of the United Nations preserves a State?s ?inherent right? of self-defence in the face of an armed attack and forms part of the definition of the obligation to refrain from the threat or use of force laid down in Article 2, paragraph (4). Thus a State exercising its inherent right of self-defence as referred to in Article 51 of the Charter is not, even potentially, in breach of Article 2,paragraph (4). … Self-defence may justify non-performance of certain obligations other than that under Article 2, paragraph (4), of the Charter, provided that such non-performance is related to the breach of that provision.”

The ILC is there invoking the ICJ’s Nuclear Weapons advisory opinion, at para. 38. See also Nicaragua case, para. 193; A. Cassese, International Law (2nd ed 2005), at 354 (stating that “Article 2.4 of the UN Charter (and the corresponding customary rule of international law) ban armed force in international relations… [A]n exception to this ban is the right of States to resort to individual or collective self-defence. This right is clearly laid down in Article 51 of the UN Charter and the corresponding customary rule of international law.”)

See further Y. Dinstein, War, Aggression and Self-Defence, 2005, at 177 (stating that “Article 2(4) promulgates the general obligation to refrain from the use of inter-State force. Article 51 introduces and exception to this norm by allowing Member States to employ force in the event of an armed attack”). See also ibid., at 205, speaking of the theoretical possibility of an armed attack emanating from a territory outside the jurisdiction of any state.

If you have an explanation as to how an exception to a rule can apply when the rule itself does not, I'd be most happy to hear it.

As for your point (2), I'm not sure whether we disagree, or whether you simply misunderstand my argument. It is possible to see the applicability of Art. 2(4) as being dependent on the motive of the state using force, as John Dehn does in this comment thread. Or, Art. 2(4) could apply whenever a state uses force against another state, which is my view, and the view of most authors.

By way of example, when the US and its allies attacked the FRY in 1999, the former theory could say that the use of force was lawful, because the states using force didn't intend to undermine the FRY's independence or territorial integrity, but acted with humanitarian purpose. That would be the end of the matter. Under the latter theory, Art. 2(4) would be engaged because any use of force against a state or in its territory without its consent would be a presumptive violation. However, if the state's using force could prove that a customary exception of humanitarian intervention has evolved, then the use of force might be justified.

Neither alternative is on its own 'clearly' true, least of all textually so, but again, the latter is in my view significantly stronger. If the latter alternative is true, that doesn't mean that every use of force is a VIOLATION of 2(4) or the state's sovereignty, merely that 2(4) is engaged, but that the use of force can be justified or excused. Thus, if the use of force was in self-defence, then it would be lawful, but it would still have presumptively engaged 2(4).

jpaust says

February 23, 2010

Its all a little more complex. Note that the ILC commentary you quote is somewhat confusing -- first, it prefers self-defense as an "exception" to the prohibition of force, but then indicates that use of 51 self-defense "is not, even potentially, in breach of Article 2, paragraph 4" -- apparently affirming that the merely three stated prohibitions of threats or uses of force in 2(4) do not reach every sort of armed force, that 2(4) does not prohibit all uses of force. See also Restatement of the Foreign Relations Law of the United States sec. 905, cmnt. g (1987) (it is generally accepted that 2(4) does not forbid limited use of force in the territory of another state al la an Entebbe-type rescue mission). During The Caroline incident, Sec. Webster noted that a fundamental rule was that states must respect the inviolable character of the territory of another state but that an "exception" arises out of the great law of self-defense -- so states were not thouht to be free of any restraints prior to the creation of the UN Charter and attention to "inherent" rights is still important (but 51 limited such to the circ. "if an armed attack occurs").

John C. Dehn says

March 25, 2010

For the record, I misspoke above. My comment says that the cited authors were "qualitative, not empirical" and what I (obviously) meant to say was "theoretical, not empirical". I should add, though, that some of those authors might be viewed as conducting, at least in part, a qualitative empirical analysis.

My view is that it would be a stretch to label the work of these authors a true qualitative analyses given the very, very small number of samples to which they refer on this topic. A better example of a qualitative analysis is the ICRC's customary IHL study. I would like to see a true qualitative or (even better) quantitative study of state practice in the area of the practice of self defense without actual ground invasion. As I said above, stand-off or aerial attacks seems to have been treated differently, when justified, and even targeted ground raids of very short duration (as Jordan mentions above) have been accepted at times.