Host State, Victim State: Problematising the ‘Unable/Unwilling’ Test

By: Ahmad Ammar and Arkaprava Dass

In February 2019, the Indian Air Force targeted the training camps of a terror group which was based in Pakistan. This measure was taken to exercise the right of self-defence against a non-state actor that was situated in Pakistan. This action highlights the response to a state harbouring terror, which is the take-off point of this article. The article seeks to establish that the ‘unable or unwilling’ test is fundamentally antithetical to Article 51 of the UN Charter pertaining to the use of force, and offers options to minimise collateral damage for both host and victim state.

Through the course of this article, we first shed light on the unilateral nature of the test and associated problems therein. Second, we establish the lack of legal basis which the test finds under jus ad bellum. Third, we point out the test’s disregard for due-diligence exhibited by the host state, thereby diluting the threshold of the prohibition on the use of force. Last, we attempt to provide the possibility of a feasible scope of application of the test in safeguarding the interests of the host as well as the victim state.


The ‘unable or unwilling’ test allows a state to lawfully use force against non-state actors who are present in another state which is unable or unwilling to suppress the threat posed by the non-state actors. The test’s earliest evidence surfaces in the pre-Charter era, in the Caroline case, when British Canada justified destroying an American steamer used to transport supplies and arms to rebels fighting the Canadian government. British Canada justified this action on the grounds of failure of the US to deal with this security threat. Today, the most obvious example of this test is when the US justified launching an air campaign on Syrian territory against the Islamic State of Iraq and the Levant in 2014. As its vindication, it cited the lack of effective confrontation by the Syrian regime against the terrorist groups present on its soil.

This use of force is indubitably suggestive of unilateral action by a state. It is pertinent to note here that the rudimentary objective of the UN Charter elucidates taking effective collective measures for the prevention and removal of threats to peace. This affirms the existence of a multilateral system based on cooperation. Unfortunately, experience shows that the spirit and letter of the Charter are typically violated in the real world.


The test has neither been incorporated in any international instrument of legally binding nature nor has it been employed by the International Court of Justice in any existing case laws. Therefore, an enquiry as to its legal basis can only be undertaken within the realm of customary international law.

First, in order for a norm to constitute customary international law, the requirement of ‘evidence of a general practice accepted as law’ has to be fulfilled. Such requirement is not met by Unable or Unwilling test as states have explicitly rejected its use. In addition, the stances of others have been ambiguous, with some implicitly endorsing the test and only a few engaging in an explicit endorsement. Uncertainty as to the existence of state practice as law defeats the legality of the norm. In the absence of a consistent stance and common opinio juris shared by states themselves that have acted in pursuance to the test, the legal validity of the test remains undecided.

Second, the Unable or Unwilling test has failed to find validation by the United Nations Security Council (hereinafter ‘UNSC’). The execution of this test was premised on the adoption of UNSC Resolution 2249 (2015), viewed as confirming the use of force in self-defence against non-state actors. However, the Resolution does not even as much as refer to self-defence, let alone mentioning the test. As an illustrative example, the reliance placed on the Resolution to justify war on Syria was misplaced. The Resolution neither authorised forcible measures under the UN Charter’s Chapter VII nor did it endorse the exercise of self-defence against Syria. Therefore, the invocation of this test on the pretext of self-defence finds its feet on slippery ground.

Implications of the acceptance of this doctrine as the law would have far-reaching effects. It challenges the notion of collective security embedded in the UN Charter framework. In other words, every state would be allowed to launch a military campaign on another state’s territory under the sole pretext of the ‘inability’ of the state to put an end to the activities of a terrorist group. 


States have a duty of due diligence to ensure that their territory is not used as a haven for terrorism. The Friendly Relations Declaration lays down that states should refrain from organising, or assisting in terrorist acts in another state, or acquiescing in organised terrorist activities within its territory. Further, UNSC Resolution 1373 obliges states to deny haven to those who finance, plan, support, or commit terrorist acts. This duty is customary.

However, the due-diligence obligation is one of conduct and not one of the results, that is, states are not required to achieve specific results as long as they act with due diligence in dealing with the threats posed by the non-state actor. The test’s justification, on grounds of violation of the duty of vigilance, concerns itself with the result that overlooks the conduct of host states tackling non-state actors in their territory. Taking into account the result-oriented approach of the test, violation of due diligence cannot be used as a justification to invoke self-defence for attacking the host state as it lowers the threshold of Article 2(4) vis-à-vis Article 51 of the Charter which speaks of the right to self-defence.


Contemporary security challenges posed by non-state actors necessarily demand a restructuring of the self-defence framework under international law. In view of the inevitability of this practice by states in endorsing, resorting to and justifying the test, a possible middle has to be conceived so as to attenuate the collateral damage.

As Ashley Deeks has opined, the primary consideration is to secure the consent of the host state to allow intervention by the victim state. But this consideration has conveniently been disregarded as a priority by the states which have made unilateral interventions into host states. If consent is denied, then the victim state must offer every possible support to the host state in neutralising the non-state actors in its territory, thus ensuring that the sovereignty and territorial integrity of the host state remains intact. In case of failure of all efforts of peaceful cooperation, indications of the unwillingness of the host state are strengthened. Possibilities of strong allegations of unwillingness on the part of host states can exist in the UNSC.

In view of the sovereign equality of all states, the determination of unwillingness is solely left to the victim state. Transparency may thus be compromised, thereby hampering the rights of the host state. Giving a free hand to states to determine the imminence of a threat, or unwillingness to use force on the territory of another state, would amount to a complete transgression of the prohibition on the use of force and the legitimate right of exercising self-defence envisaged under the Charter. In such an event, a formal enquiry may be protracted, however, going as per cost-benefit analysis, the rights of the host state and the victim state will be balanced in a legitimate manner.


Unilateral action poses a constant threat to international law. The ethos of the UN Charter is such that it limits the unilateral use of force. This is evident from the text of Article 51 of the Charter which recognises “the inherent right of individual or collective self-defence until the Security Council has taken measures necessary to maintain international peace and security”. In the absence of the unable or unwilling test fulfilling an appropriate legal basis for action, it becomes essential to ensure that execution of the test does not go against the spirit of the Charter. The aforementioned suggestions carried out in their true sense would alternatively effectuate the emergence of trends and practices which would manage the implications of the test in an improving manner.

(Ahmad and Arkaprava are currently undergraduates at Faculty of Law, Jamia Millia Islamia, New Delhi.)

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