The ‘Unwilling or Unable’ Test and the Law of Self-defence

Abstract

Recent events related to the rise of ISIS have catapulted the ‘unwilling or unable’ test to the forefront of the legal debate concerning the fight against terrorism. The still controversial test offers a justification for unilateral use of force in self-defence on behalf of a victim state on the territory of a host state that is unwilling or unable to prevent a non-state actor located on its soil from carrying out attacks against the victim state. The aim of this chapter is to analyse the history, current status and content of the ‘unwilling or unable’ test with a view to highlighting the main concerns that come with it. This chapter argues that if the ‘unwilling or unable’ test is here to stay, governments and authors alike must make considerable effort to clarify its content, delineate its limits and set out its requirements in the context of the law of self-defence. Subject to evolving state practice, the ‘unwilling or unable’ test may fit into the necessity requirement of the law of self-defence. If so, emphasis should be put on the victim state’s duty to show, by way of a thorough assessment, the host state’s continuous and evident unwillingness or inability to prevent terrorist organizations from using its territory. This requirement should only come after the victim state has shown that the occurred or imminent armed attack creates an immediate need for action. In any case, measures based on consent, which would circumvent the need to apply the test, should always be prioritized. To present its argument, Sect. 4.2 will embark on a brief review of relevant (state) practice. Next, it will assess the current status of the test on the basis of the conducted review. Section 4.4 will look into the anatomy of the ‘unwilling or unable’ test and Sect. 4.5 will analyse the use of the test in relation to the US-led intervention in Syria to neutralize ISIS targets.