The Seemingly Inexorable March of “Unwilling or Unable” Through the Academy

by Kevin Jon Heller

How does an international-law doctrine become conventional wisdom without actually having support in the practice of states? It starts with one article asserting the doctrine, but failing to defend it. Then another article makes the same claim, citing only the first article. And then another. And another. And so on — until no one remembers that the first article did not actually identify any state practice at all.

So it is with the “unwilling or unable” test, as indicated by an otherwise quite good new article in the Journal of Conflict & Security Law entitled “Jus ad Bellum and American Targeted Use of Force to Fight Terrorism Around the World.” Consider (p. 228):

With regard to the use of self-defence against private actors located in another state, two consequences flow from the requirement of necessity. First, state practice indicates that the exercise of self-defence against the private actor is conditioned on the inability or unwillingness of the authorities in the host state to stop the private actor’s activities.98 Obviously, if the host state both can and will stop the activities in question, it will not be necessary for the victim state to resort to the use of force.

I’ve left the footnote number in, because it refers to precisely one source: Ashley Deeks’ essay “Unwilling or Unable: Toward an Normative Framework for Extra-Territorial Self-Defense.” An essay in which, as I have pointed out, the author openly admits that she “found no cases in which states clearly assert that they follow the test out of a sense of legal obligation.” (The US and UK have formally endorsed the unwilling or unable test since Deeks’ article was published.)

To be sure, the new article elaborates a bit on the “support” for the unwilling or unable test. But none of that support involves the practice of states — nor does the article acknowledge the inconvenient fact that the Arab League (22 states) has formally rejected the test (post-9/11, even). Instead, it simply says this (p. 229):

The test is widely supported in the literature, and it is also mentioned in two 2013 UN reports by, respectively, the UN Special Rapporteur on extrajudicial, summary or arbitrary executions and the Special Rapporteur on the promotion and protection of human rights and fundamental freedoms while countering terrorism. It also features among a series of “Principles Relevant to the Scope of a State’s Right of Self-Defense Against an Imminent or Actual Armed Attack by Nonstate Actors” proposed by the former legal adviser of the United Kingdom Foreign & Commonwealth Office, Daniel Bethlehem.

“Instant custom”? How passé. Who needs state practice at all? And please don’t bore us by pointing out contrary practice by a bunch of benighted states in the Global South. All we really need are enough scholars, special rapporteurs, and former legal advisors in the Global North willing and able to endorse a particular doctrine and poof — customary international law.

10 Responses

  1. I agree that the so-called test is not a limitation of the inherent right of self-defense under customary international law or Article 51 of the UN Charter. But if the rockets are flying across the border, for that time at least, the foreign state is decidedly “unable.” Finally published: Operationalizing Use of Drones Against Non-State Terrorists Under the International Law of Self-Defense, 8 Albany Govt. L. Rev. 166-203 (215), available at

  2. Thank you Kevin for drawing attention to the troubling methodology by which self-interested behavior of elite states is “legalized” through the assertion that it is “custom” (or at least attempted to be transformed into lawful behavior). Troubling too is how the meaning of “several’, “many”, and “frequent” are misappropriated to refer to the acts of two or three states. All states are equal but some are more equal, I guess. Still, Deeks, Kress, and Henriksen’s papers are great contributions to the thinking on this issue. It seems to me, however, that the value of their research and contributions could have stood independently (and perhaps even stronger) (e.g. Deeks articulation of substantive and procedural factors) without having to force “unwilling or unable” into a customary rule.

  3. Shahram,

    I couldn’t agree more. Kress and Henriksen’s articles are otherwise excellent, and Deeks’ article is a fine articulation — from a normative perspective — of what unwilling/unable would look like as a test. The problem, as you note, is that they all claim unwilling/unable is lex lata when, in fact, it is lex ferenda.

  4. Great post. Soft law is undermining the development of badly needed, enforceable agreements by creating the dangerous, “poof” illusion of progress for political bodies to hide behind. Actual, documented conduct is then conveniently ignored for political expediency.

  5. Prof Heller, the sources the Ruys book (which is referred to in the previous post) relies upon to prove the Arab League rejection of the unwilling or unable test do not actually express a formal rejection of that test. Instead, the Arab League States condemned what they called Israeli “aggression” against Lebanon. This may relate to perceived dis-proportionality, lack of intensity for an armed attack and more. It does not necessarily expressly or implicitly indicate a rejection of the unable or unwilling test.

  6. Feel free to send me the document with the position of the LAS. If Ruys is wrong, I will amend the post.

  7. Here is the link to the UNSC discussions cited by Ruys:
    Here is a link to the text of the LAS resolution which is referred to in the discussions:

  8. Kevin, Ori,

    Thank you for your interesting comments. What I wrote in the book (452-453) was simply that the League of Arab States condemned the Israeli aggression, not that it specifically rejected the unable and unwilling test. Overall, I found that back in 2006 (1) a majority of the international community regarded the self-defence claim of Israel as valid in principle, and; (2) that criticism focused almost exclusively on the obviously disproportionate character of Israel’s Operation ‘Just Reward’ (at 453). Accordingly, while I fully agree with Kevin that the need for a detailed and honest assessment of State practice and opinio juris is sometimes passed over too lightly, I do believe the 2006 Lebanon war offers a precedent that can validly be invoked to support the unable and unwilling doctrine. By contrast, several other incidents (e.g., Colombia’s Operation Phoenix) seem to reveal a more ambiguous position vis-à-vis the idea of a broadened right of self-defence against non-state actors (no longer dependent on any test of State imputability) – which is why I concluded that we seem to be witnessing an evolution de lege ferenda (!)of customary international law (530-531).

    What is particularly interesting with regard to the US-led operation against IS, is that this is probably the first precedent since 2006 which gives us insight into the legal positions of a considerable number of States in respect of self-defence against non-State actors. An overview of relevant State practice and opinio juris in this respect can be found in the upcoming ‘Digest of State Practice’ to be published shortly in the next issue of the Journal on the Use of Force and International Law ( Here is one excerpt, for instance, which readers may find interesting:

    “In a letter to Parliament, the Dutch government justified the troop deployment on the basis of the request for military support from the Iraqi authorities of 25 June and 20 September 2014. This request was stated to provide sufficient legal basis for the deployment of forces within Iraq. As far as military operations within Syria are concerned, the letter states that there is ‘currently no international consensus on the question whether there is a legal basis under international law for military action in Syria’ (our translation). The letter acknowledges that there are no longer clear boundaries between Iraq and Syria, and that IS presence in Syria poses a direct threat to Iraq. The letter expresses understanding for the American efforts against IS in Syria, while observing that the US has invoked the right of collective self-defence under Article 51 UN Charter. On the other hand, it is noted that:
    ‘strict conditions apply for the exercise of this right, especially when an (imminent) armed attack emanates from an armed group such as IS. What is determining then is whether or not Syria is able or willing to tackle such attacks. At this moment it cannot be ascertained whether or not self-defence provides an international legal basis. The Dutch troop deployment is therefore limited to Iraq.’” (See (2014-2015) Staten-Generaal Doc. 27 925, Nr. 506, 4-5)

    One other thing: with all due respect for Ashley Deeks, the ‘unable and unwilling’ test is not something she invented out of thin air in 2012. Several references to some sort of ‘unable and unwilling’ test can be found in State practice long pre-dating the 9/11 attacks. Israel already invoked it, for instance, in the late 1970s and early 1980s to justify military operations in Lebanon. It has also been invoked in the context of the ‘protection of nationals’ controversy. Consider the statement by the US in the Security Council debates following the Entebbe operation: ‘there is a well established right to use limited force for the protection of one’s own nationals from an imminent threat of injury or death in a situation where the State in whose territory they are located is either unwilling or unable to protect them’. One can go even further back in time. See e.g., the account of the ‘Amelia Island’ incident in Oppenheim (1912, 2nd ed., § 132 (dealing with ‘self-preservation’): ‘The Spanish Government not being able or willing to drive them off, and the nuisance being one which required immediate action, President Monroe … directed that a vessel of war should proceed to the island and expel the marauders…’).

    In any case, even if the unable and unwilling test may not (yet) be part of lex lata, recent evolutions suggest it is here to stay. The key challenge is perhaps to define this doctrine in such a manner as to properly balance the interests of the intervening State and the territorial State – and to avoid it becoming a recipe for abuse and for the further spreading of State failure.

  9. Tom,

    Thanks for the comment. Between you and Ori, I obviously need to stop referring to the LAS reaction to Israel’s actions in 2006 as a rejection of the unwilling or unable test. But I’m curious, having quite carefully read the documents Ori linked to: on what basis do you believe that the general response to Israel’s actions affirmatively supports the test? The documents seem to indicate that many states (including Israel) thought Hezbollah was acting on behalf of Lebanon — which means that this was not a situation in which either (1) Israel was claiming a right of self-defense on the ground that Lebanon was unwilling or unable to stop Hezbollah, or (2) other states were affirming the right to act in self-defense against a non-state actor whose armed attack was not attributable to a state. I’d appreciate your thoughts.

  10. Kevin,

    I don’t think ‘many States’ considered Hezbollah to be acting ‘on behalf of’ Lebanon. True, Israel suggested the 12 July attack was the action ‘of a sovereign State’, but at the same time Israel itself acknowledged Lebanon’s problem was mainly one of inability to disarming and dismantling Hezbollah.
    Furthermore, numerous States, rather than holding it responsible for the attack, expressed sympathy for the Lebanese government (see also SC Res 1701(2006)).

    It is fair to state that the Security Council debates do not provide explicit verbal support for the unable and unwilling doctrine as such, but when putting the pieces together the fact remains that (1) the Hezbollah attack was not imputable to Lebanon under the traditional law of State responsibility; (2) the majority of the international community did accept that Israel could rely on the right of self-defence, and; (3) the acceptance of the self-defence claim was inspired by the fact that Lebanon was unable to prevent cross-border attacks against Israel.

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