Applying the International Criminal Court’s “Unwilling or Unable” Test to Extraterritorial Self-defense Against Non-state Actors in Light of Acquiescence

In international law, as it stands crystalized today, no consensus on the existence of the right to self-defense against non-state actors (NSAs) has been reached, as it does not fall within the scope of Article 51 of the United Nations Charter. It is, however, a right highly debated and some scholars interpret the existing framework to argue for its existence.

The Unwilling or Unable (UoU) test justifying self-defense against NSAs is controversial and not internationally accepted as custom. It is, however, sufficiently supported by states to be considered lex ferenda. Perhaps a reason for this lack of unanimous support is the ambiguity of the requirements under which the test is applicable, and even more so the sources from which these requirements are derived. Therefore, this essay will purport to draw an analogy with Article 17 of the ICC Statute, on the basis of the principle of sic utere tuo ut alienum non laedas (“Use your own property in such a way that you do not injure other people’s”) and in light of acquiescence in order to clarify these requirements.

Basis for analogy

Despite seemingly different contexts, both Article 17 of the ICC Statute and the right to self-defense under Article 51 of the UN Charter are the means to the same end. This is the hierarchy in which entities, be it states or organizations, can respond to breaches of international law.

The rationale behind Article 17 of the ICC Statute is that it is every state’s duty to prosecute international crimes in the territory under their jurisdiction. If the state normally exercising jurisdiction over the act is unwilling or unable to do so, and endangers international security by promoting impunity, the ICC intervenes. This is closely interrelated with sic utere principle; i.e. the state, by allowing for its territory to be used as a means for committing international crimes injuring others, while responsible to prosecute, is in breach of the aforementioned principle; therefore relinquishing a portion of its sovereignty.

Similarly, when a state allows an NSA to use its territory in launching attacks against another state, the principle of sic utere is breached by the former. This could potentially allow for the injured state to determine the unwillingness or inability of the host state to prevent such usage of its territory, and, analogous to the ICC, take unilateral action. Moreover, recalling that states have a responsibility to protect their own populations, whereas the ICC bears no responsibility, states’ self-defense must a fortiori be permitted on the basis of the sic utere principle. This is a general principle of law under Article 38(1)(c) of the International Court of Justice (ICJ) statute and was applied in several cases, including the Corfu Channel case.

Requirements and Application

Having established the basis for analogy, I will hereinafter attempt to clarify the requirements of the UoU test.

In clarifying the UoU test, the ICC has confirmed that either inability or unwillingness will result in inactivity on part of the state who would normally exercise jurisdiction. Moreover, even if the activity on part of the state exists, if it is in a manner so as to shield the person from criminal responsibility, and in a manner inconsistent with an intent to bring the accused to justice, or in case there has been an unjustified delay, the state is considered unwilling to act. Additionally, in clarifying inability, one must take into account the national judicial system of the state.

In applying the aforementioned criteria to the creation of the right to self-defence, it must be primarily determined whether the host state has been active towards the NSAs using its territory in their conduct against the injured state;

  1. a) If there exists such activity, it should have been one that is factitious, and shall not be an actual attempt to contain the activity of the NSAs. Failing such activity, it must be taken into account whether any preparation for the containment of the NSAs has been made, and if so, the action to be followed by such preparation must be unduly delayed.
  2. b) In case no action has been taken, taking into consideration the military capacity of the host state, it must not be beyond its ability reasonably to contain NSAs.

In case the host state is neither unwilling in accordance with paragraph (a) above, nor unable in accordance with paragraph (b), it has shown good faith in its duty towards the injured state. Clearly, in such a situation, the host state has been active and its activity has resulted in the seizure of the NSA’s attacks. Therefore, there shall exist no right of extraterritorial self-defense for the injured state unless with the consent of the host state under article 20 of ARSIWA; an interpretation of which will be offered in the next section.

The acquiescence of the Host State

As defined by the International Court of Justice (ICJ) in the Gulf of Maine case, “…acquiescence is equivalent to tacit recognition manifested by unilateral conduct which the other party may interpret as consent…”.

Where silence, on an occasion where there was a duty or need to speak or act, implies agreement, or a loss of rights, and can be regarded as a representation to that effect, the principle of acquiescence is accompanied by estoppel. Therefore, the absence of reaction may well amount to acquiescence.

I argue in alternative to my interpretation of the UoU test, that the mere inactivity of the host state while required under the sic utere principle can amount to acquiescence and be interpreted as consent for the injured state to act, as follows.

Article 20 of the ARSIWA enshrines, “Valid consent by a State to the commission of a given act by another State precludes the wrongfulness of that act in relation to the former State to the extent that the act remains within the limits of that consent.”

States have the right to dispense with the performance of an obligation owed to them individually. This means that while the obligation under article 2(4) of the UN Charter persists, the host state can waive the performance owed to it thereof. This is reiterated by article 45(b) of the ARSIWA. The article emphasizes that the conduct of States, and where applicable, unreasonable delay, is the determining criterion for the lapse of the claim. A claim will be inadmissible on grounds of delay where the circumstances are such that the state should be considered as having acquiesced in the lapse of the claim or the respondent State has been seriously disadvantaged. Therefore, inactivity or undue delay for action on part of the host state can amount to acquiescence and preclude the wrongfulness of the injured state’s use of force in its territory against the NSAs.

When observing the situation surrounding an injured state under attack by an NSA located on another state’s territory, all the aforementioned criteria are fulfilled. The undue delay to conduct on part of the host state, whether resulting from being unwilling or unable, where the action is required in accordance with the ICJ’s definition, amounts to acquiescence. Failing that, the injured state whose territory is under an attack it legally can’t defend has been seriously disadvantaged seeing as its essential interest has been violated and needs to be protected.


Undoubtedly, a state under attack by NSAs is in a state of necessity and the existence or the belief of the existence of such criteria must only be established in a subsequent communique to the Security Council. It is briefly reiterated, however, that I am of the opinion that this particular case of acquiescence acts as estoppel and precludes objection by the host state of the injured state’s actions nonetheless. I am aware of the dangers to the prohibition of the use of force this interpretation brings, and note that the interpretation must be used restrictively and with caution.

Ultimately, recognizing the different contexts of jus ad bellum and international criminal law, I believe that with the goal of the progressive development of international law, fundamentally similar concepts can be drawn from the more developed fields and applied to the less developed. These criteria, as opposed to ones set forth previously, have a strong legal basis in states’ negotiations in drafting the Rome Statute, including all but one state of those in explicit or implicit support of the UoU test, therefore potentially enjoying universal support.


Bahar Babapour is an Iranian LLM candidate studying Public International Law at the University of Amsterdam and a member of the Amsterdam Criminal Justice Clinic in 2020-21, conducting research upon assignment of a UN organ.