Why Unilateral Humanitarian Intervention Is Illegal and Potentially Criminal

by Kevin Jon Heller

I read Jennifer Trahan’s post yesterday with great interest — but not surprisingly I disagree with it. Before I get to my disagreements, though, I think it’s bizarre that we are all debating the legality of unilateral humanitarian intervention in the context of the recent US missile attack on Syria. It simply beggars belief to think that the attack was in any way motivated by humanitarian concerns. Chemical weapons, which have killed perhaps 2,000 civilians, are not the problem in Syria; conventional weapons, which have killed hundreds of thousands, are the real threat. And the US has done absolutely nothing to protect Syrians from conventional weapons — it has simply funnelled even more into the country to support various rebel groups (including some that are allied with al-Qaeda) in their struggle against Assad. The US cares about protecting its own interests in Syria, such as preventing chemical weapons from being used against Americans. (The real message of the completely ineffectual attack.) It does not care about the lives of ordinary Syrians, as the ever mounting death-toll indicates.

But let’s put aside the context of the missile attack and focus on Trahan’s legal claims. The first is that unilateral humanitarian intervention (UHI) — the qualifier, of course, is critical — can be legal in the right circumstances. The post, however, doesn’t even come close to establishing that claim. Just consider what Trahan cites in defence of it:

[1] NATO’s intervention in Kosovo, in which “all NATO members supported the intervention designed to stave off ethnic cleansing.” Trahan openly acknowledges that “many did not defend it as ‘humanitarian intervention’ per se, except Belgium” — but that gives away the ballgame. If the 26 other NATO states did not invoke UHI, the attack does not help establish UHI’s legality. As the ICJ pointed out in the Nicaragua case (para. 207), not even the Court itself has the “authority to ascribe to States legal views which they do not themselves advance.” So it doesn’t matter whether Trahan and other scholars would like to describe Kosovo as an example of UHI. All that matters is that NATO states could have invoked UHI but chose not to.

It is also telling that Trahan fails to point out that the Kosovo intervention met with significant international criticism. Here are Vaughan Lowe and Antonios Tzanakopoulos in the Max Planck Encyclopedia:

33  The response of other, non-NATO, States to arguments that there was a legal basis for the Kosovo bombing campaign and for a right of humanitarian intervention was overwhelmingly negative. The Non-Aligned Movement (NAM), numbering well over half of the Member States of the UN, unequivocally condemned the use of force against the (then) FRY, as did many other States, some of which are nuclear powers. In these circumstances, no right of unilateral forcible humanitarian intervention can be said to have emerged as a rule of customary international law.

[2] UK and US no-fly zones in Iraq. Once again opinio juris is lacking: the coalition initially provided no legal justification for the no-fly zones, and the US later justified them as self-defence (against threats to coalition aircraft, a wonderfully circular argument).

[3] ECOWAS’s interventions in Liberia in 1990 and Sierra Leone in 1998. Same problem: as Adam Roberts has pointed out, ECOWAS never invoked UHI to justify its actions. It relied instead on provisions in its own founding treaty.

[4] The UK’s endorsement of UHI in Syria, particularly in the context of the 2013 sarin gas attack that killed hundreds if not thousands. Unlike the other examples, this endorsement does, in fact, contribute opinio juris in favour of UHI.

So, there we have it: one state that explicitly and regularly endorses a right of UHI.  And against that, we have the unequivocal rejection of UHI by the 120 states that are part of the Non-Aligned Movement and the 134 states that are part of the Group of 77, which includes major powers like China, India, and South Africa. (The two groups obviously overlap.) How any scholar could conclude that customary international law nevertheless recognises a right of UHI, however limited, is simply beyond me.

For similar reasons, I also reject Trahan’s confident claim that UHI could never be criminal. Here is what she says:

Humanitarian intervention, narrowly construed, then clearly also would not constitute the crime of aggression, which is poised to activate this December 2017 before the International Criminal Court. (Anything in a legal “grey area” is excluded from that definition—and, at minimum, humanitarian intervention (sometimes supported and sometimes invoked) is within that legal grey area. The U.S., a non-State Party to the ICC’s Rome Statute, would be exempt from the crime’s jurisdictional reach, even if it does activate.)

I disagree. To begin with, during the Kampala Review Conference in 2010, states soundly rejected the US’s attempt to specifically exclude UHI from the crime of aggression. Here is the text of the US’s failed Understanding:

It is understood that, for purposes of the Statute, an act cannot be considered to be a manifest violation of the United Nations Charter unless it would be objectively evident to any State conducting itself in the matter in accordance with normal practice and in good faith, and thus an act undertaken in connection with an effort to prevent the commission of any of the crimes contained in Articles 6, 7 or 8 of the Statute would not constitute an act of aggression.

More importantly, the fact that scholars insist UHI can be legal does not make the legality of UHI fall into a “grey area.” On the contrary, it is difficult to imagine any issue that is more black and white given state practice. Article 2(4) of the UN Charter is clear: force is legal only when authorised by the Security Council or in self-defence. UHI does not involve the former by its very definition, and there is no argument de lege lata that UHI can be justified as a form of self-defence, because it does not involve an armed attack on the intervening state. Adil Haque made that point in response to Jens’s recent post, and here are Lowe and Tzanakopoulos again:

23  Humanitarian intervention in order to alleviate the suffering of a local population cannot, without more, be justified as self-defence. Self-defence under Art. 51 UN Charter requires that an armed attack occur against a State. In most cases, widespread violations of human rights will not reach the gravity threshold of an armed attack. Even if the oppression does reach the threshold of an armed attack, however, there will be no armed attack against a State, but at most an armed attack against the population of the State by or with the support or inaction of State authorities. The right to self-defence under international law vests in States and not in sub-State entities such as the local population. Moreover, the oppression will, ex hypothesi, not emanate from another State, but will be by the government upon its own people.

The illegality of UHI under Art. 2(4) is, of course, not set in stone. As Lowe and Tzanakopoulos rightly note, UHI could become legal through subsequent state practice that results in a new interpretation of the provision or (possibly) through the emergence of a supervening customary rule. But that has clearly not happened, given G77 and NAM’s ongoing and unwavering opposition to UHI.

It is unlikely, of course, that the ICC will ever prosecute a government official who is responsible for preparing, planning, initiating, or executing a UHI — and not simply because of the new crime of aggression’s crimped jurisdictional regime. But that does not mean UHI does not manifestly violate the UN Charter. It most certainly does.


18 Responses

  1. A few quick responses to Kevin:

    We don’t know the motivation of the US missile strike, as we don’t have a clear articulation of legal doctrine by the US administration. It would be helpful if the US would make the case.

    Agreed, the greater death toll is not chemical weapons attacks, and the international community (I won’t only blame the US) has done nothing to help protect the Syrian people from these. We should not only be concerned with chemical weapons use.

    Assisting the rebel groups is indeed complicated by the composition of some of the groups

    That other states did not openly embrace UHI at the time of NATO is not an indication of lack of buy-in to the concept. There were NOT other strong plausible alternatives why they were using force. I am arguing that they implicitly bought into the legal theory. (In the briefing to the ICJ, most stuck to arguing lack of jurisdiction, so as a tactical point at the ICJ, chose not to brief the merits.)

    The AU’s Constitutive Act and ECOWAS Protocol basically justify ECOWAS humanitarian intervention.

    And Kevin’s focus on rebutting UHI is unwarranted, as I clearly argue that is the LEAST best way to respond. That is the worse approach for doing HI. I am clearly defending the concept of HI.

    Did I say “UHI could never be criminal”? Nope, Kevin, read my post again. There definitely could be pretextual invocations that could be. I have an entire 50 page article on the topic: Check it out: “Defining The ‘Grey Area’ Where Humanitarian Intervention May Not Be Fully Legal, But is Not The Crime of Aggression,” 2 Journal on the Use of Force and Int’l Law 42 (2015)

    The US understanding was not accepted at Kampala. No debate about that. We then can debate what that implies. It implies to me that in the very limited time allocated (I was at Kampala) to the negotiation of understandings, in the way that it was formulated (overbroadly), and given all the other understandings that had to be agreed upon, it was not accepted. So, there isn’t that much “take away” from that.

    My case was not for UHI, but for HI. A bona fide, HI would most certainly not constitute a “manifest” Charter violation for a whole host of reasons. See my article.

    But, Kevin: more to the point: what is your answer? Go back to Kofi Annan’s question and tell me what you would do when the UNSC is sitting on its hands?

    It is easy to be critical of the HI arguments (even moreso the UHI arguments), but what is needed is for the armchair academics to suggest helpful alternatives.

  2. Kevin,

    Why the qualifier “potentially” next to the term criminal? It seems like your view is that it violates jus ad bellum and that there is no criminal law excuse for humanitarian interventions. Under what circumstances would you exclude criminal liability for aggression?

  3. The L & T quote puts the disagreement nicely. They claim that international law affords no right of self-defense to local populations. I think it does when they are subject to an unlawful attack. Indeed, I find it a bit shocking for someone to say that local populations are not entitled to a right to self-defense when faced with illegal attacks that violate international human rights law, international humanitarian law, and international criminal law.

    States have the right to put down rebellions but don’t have the right to violate IHL, IHRL, or ICL in the process. When they do so, their attacks constitute an armed attack against their own people, which triggers a right of self-defense in response from those people.

    Just to be clear what is at stake here. The orthodox view is that a dictator could kill almost his entire population and, in the absence of the SC Res, the world community is not allowed to intervene.

  4. Indeed, I would also note that even ICL recognizes an individual right of self-defense under some circumstances. So the claim that “international law” does not recognize a right of self-defense for local populations (quote from the MP treatise) is an overbroad statement.

  5. Jennifer notes that “We don’t know the motivation of the US missile strike, … .” In such circumstances, it is hard to see how a missile strike could be considered a humanitarian intervention that is consistent with international law.

  6. As to what should be done instead of UHI, I would suggest making the case for a particular intervention to other governments, and gathering a coalition in support before any action is taken. If you can’t convince at least 30 or so — and more is better — countries that what you are doing is justified, perhaps it shouldn’t be done.

  7. Hi all,

    I’ll leave Jennifer and Kevin to duke it out . . . except to say that I also find it “bizarre that we are all debating the legality of unilateral humanitarian intervention in the context of the recent US missile attack on Syria.” I suspect that we are doing so because this debate feels familiar, while the reality that we face is not.

    Just a quick thought for Jens: I worry that you’re conflating national self-defense and personal self-defense. The UN Charter (and the Lowe and Tzanakopoulos quote) is about the use of force between States, not the use of force between persons.

    Let’s grant that persons have an IL right to personal self-defense against other persons—including State officials whose acts violate IHL, IHRL, or ICL as the case may be. (Jan Hessbruegge has a newish book on the topic, which I look forward to reading.)

    Let’s also grant that international law does not prohibit you, as a person, from helping other persons exercise their right of personal self-defense. So, if you want to go to Syria and fight ISIS or the Assad regime, IL does not prohibit you from doing so.

    It doesn’t follow that States may use force against other States to help persons exercise their right of personal self-defense. According to the UN Charter, States may use force against other States only in national self-defense, individual or collective, “if an armed attack occurs against a Member of the United Nations.”

    Of course, we could change international law to permit States to use force against other States in defense of persons as well as in defense of States. I would be quite open to such a proposal, although of course I would want to know the details.

    All the best,


  8. I wasn’t conflating individual and national self defense. I was noting that ICL is a creature of international law.

  9. Also, I don’t think the personal defense has any territorial limitations either.

    It’s an odd result: the state is responsible but the individuals might have a justification. Not a paradox per se.

  10. Jennifer,

    And Kevin’s focus on rebutting UHI is unwarranted, as I clearly argue that is the LEAST best way to respond. That is the worse approach for doing HI. I am clearly defending the concept of HI.

    If you believe that any humanitarian intervention that is not approved by the Security Council is unlawful, we don’t disagree. But I think it’s clear you are arguing that, in certain narrow circumstances, intervention is lawful even in the absence of Security Council referral — which is UHI, not HI, no matter how limited the intervention might be. And for the reasons that I explain in the post, I reject that idea.

    Did I say “UHI could never be criminal”? Nope, Kevin, read my post again. There definitely could be pretextual invocations that could be. I have an entire 50 page article on the topic: Check it out: “Defining The ‘Grey Area’ Where Humanitarian Intervention May Not Be Fully Legal, But is Not The Crime of Aggression,” 2 Journal on the Use of Force and Int’l Law 42 (2015).

    I never claimed that you believe any and all unilateral humanitarian intervention is legal — even the pretextual kind. But both your post and your article (which I’ve read) clearly argue that certain kinds of humanitarian intervention are excluded from the crime of aggression because they are not “manifest” violations of the UN Charter. And I reject that idea, no matter how “bona fide” the intervention might be: because unilateral humanitarian intervention does not respond to an armed attack, it is not even arguably self-defence and thus manifestly violates Art. 2(4). Full stop. I know you disagree, but I have not mischaracterized your argument.

    But, Kevin: more to the point: what is your answer? Go back to Kofi Annan’s question and tell me what you would do when the UNSC is sitting on its hands?

    My position is the one that Marko Milanovic recently articulated to brilliantly at EJIL: Talk! — namely, that although UHI is never lawful, I can imagine a situation in which a genuinely well-intentioned leader (ie, not Donald Trump) should be willing to break the law and suffer whatever consequences doing so entails. I am also very much in favour of the ACT Code of Conduct, though I don’t share your faith in the US’s empty rhetoric about the importance of deterring atrocity. (Which only applies when the atrocities are being committed by an unfriendly regime.) And, of course, I would love to see the kind of Security Council reform that would eliminate P-5’s veto in toto.

    It is easy to be critical of the HI arguments (even moreso the UHI arguments), but what is needed is for the armchair academics to suggest helpful alternatives.

    It’s even easier to advocate force as a solution to humanitarian crises, even though it rarely if ever works and rarely if ever is actually motivated by humanitarian concerns. Better to be an “armchair academic” who defends international law than one who encourages the US to bomb yet another Middle Eastern country in violation of the UN Charter. Those bombs may help assuage liberal guilt, but they do nothing to prevent atrocity.

  11. Why should PIL take precedence over ICL? People keep saying it’s illegal under international law. Isn’t that an omission? Why not say it’s justified under ICL? That’s equally true, isn’t it? The full answer is that it’s illegal under one body of international law but potentially lawful under another body of international law.

    I’m still a bit troubled by the fact that the doctrine, under the orthodox view, suggests that the state acts wrongfully while the individuals who make up the state act rightfully. It’s not just that the individuals are excused — they are potentially justified. Strikes me as very strange that when you aggregate a large number of justified acts together you get an unjustified act at the collective level.

  12. Hi Jens,

    Tell me if this is a good summary of your view:

    (i) A leader who satisfies the elements of the crime of aggression (eg, 8bis) may assert defense of another person (eg, 31(1)(c)) as an affirmative defense in cases of humanitarian intervention;

    (ii) Yet, under the Charter, a State may not use force against another State solely in defense of persons in the other State in cases of humanitarian intervention;

    (iii) It is incongruous for a leader to be justified in ordering a use of force under ICL but the State to be unjustified in carrying out that use of force under PIL.

    Is that right?

    All the best,


  13. Yes, although I wouldn’t describe it as a view — more of a question.

  14. Responding again to Kevin,

    Yes, I do argue that in certain circumstances HI is lawful without Security Council approval. I assume by UHI you mean “unilateral” HI? That would be my last resort, preferring HI by a regional actor as 2nd best, and a coalition as 3rd best. I am not sure our acronyms are picking up those nuances.

    Oh, so glad you read my article! That warms my heart. Many scholars endorse the view that certain kinds of humanitarian intervention are excluded from the crime of aggression because they are not “manifest” violations of the UN Charter. Crime of aggression under article 8bis, para 1 requires a “manifest” Charter violation by its “character, gravity and scale.” Gravity and scale eliminate lesser incursions (below a de minimis threshold), and “character” eliminates anything in a “grey area of legality.” We have years of travaux saying that. I argue, at minimum, HI falls in that “grey area of legality,” as do many others. So something COULD be a Charter violation, but still not encompassed by the crime of aggression, which has a threshold that has to be triggered.

    I don’t know the US Administration’s current intentions, as they have not articulated them, so it is hard to assess whether they are well-intentioned or not. But I don’t think the answer is telling the leader to break the law. As international lawyers, we must be able to think of something better than that.

    I think maybe we need to go back to the drawing board. I don’t think the law is sufficiently answering Kofi Annan’s original question.

    Will the US missile strikes convey a warning? Quite possibly. I think it is too soon to say it will do nothing to prevent atrocities.

    What I think is sorely needed however is MORE than the missile strikes, in terms of sustained committed engagement to alleviating the refugee crisis (including the US accepting refugees), working towards a political solution (possibly involving partitioning), and eventually war crimes trials — for instance through a regional hybrid tribunal, formed via the General Assembly and countries in the region,as David Scheffer has been advocating.

  15. While I don’t think a bona fide HI reaches the “manifest” threshold, assuming that it did for the sake of argument, I have thought of a few arguments why it still would not make a good ICC case:
    * Doubt about legality should be construed in favor of the accused. RS art 22(2) (in dubio pro reo).
    * Requirement of proof beyond a reasonable doubt and presumption of innocence (art 66) – only strong cases to being with.
    * The purposes of the ICC is to try the most serious crimes. Art 1, preamble.
    * Considerations of “gravity” and “the interests of justice” should also suggest only bringing strong cases
    * The ICC’s institutional credibility. If there were something that looked like legit (bona fide) HI (e.g. meting criteria) that the ICC attempted to prosecute, I think the ICC would take a credibility hit.
    * The application of other bodies of law (art 21) the judges also (in addition to RS, Elements, RPE) apply “applicable treaties and principles and rules of int. law”. So should consider RS harmoniously w both R2P and HI.
    Other arguments suggest there could be affirmative defenses:
    * A state of necessity” — this “justifies the violation of a binding rule in order to safeguard, in [the] face of grave and imminent peril, values which are higher than those protected by the rule which has been breached.” (Belgium in Yugo (FRY) v Belgium)
    * Mitigation.
    * Justification, excuse/ motive
    * Self-defense or duress. [Others suggest – I don’t think HI usually will be self-defense or duress]
    * Superior orders for all but top accused
    * Lack of mens rea – good faith humanitarian intervention
    * Possibly, mistake of law

    But, the last two arguments still need to reconcile with “manifest” being an objective qualifier (it doesn’t seem to look at subjective state of mind).

  16. Hi Jens,

    It’s a good question! I posed it to Roger Clark over the weekend. He was quite firm that art 31 wasn’t intended to apply to the crime of aggression (which of course hadn’t been drafted yet). It was mostly about soldiers using force against civilians engaged in criminal violence but not directly participating in hostilities. But it’s an interesting idea. Hope you continue to work on it.

    All the best,


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