The Gaza war, which started on 7 October 2023 through the horrendous attack by Hamas on Israel, has caused a depressing measure of human suffering on all sides. As far as Israel’s use of force is concerned, this war also constitutes a challenging case for the application of the jus contra bellum. This chiefly arises from the genuine legal uncertainty concerning the applicability of the right of self-defence when an armed attack by a non-state organisation emanates from the territory of a state that has proven unable to prevent said armed attack. Arguably, the situation in the Gaza Strip on 7 October 2023 presents the rare variation of such an ‘unable host state scenario’ where the non-state armed attack (by Hamas) against a state (Israel) has originated from a territory (the Gaza Strip) destined for the realisation of the right to self-determination of a people (the Palestinian people). In such a case, the dilemmatic conflict that underlies the uncertainty about the applicability of the right of self-defence is between the legally protected interests of the state that is the victim of the armed attack and those of the ‘host people’ of the non-state attacker.

On 23 September 2014, the United States of America sent a letter to the Security Council justifying the launch of an air campaign against the Islamic State of Iraq and the Levant (ISIL) on Syrian territory. In this letter, the US referred to a formula that appeared a few years ago in certain scholarly writings: the ‘unwilling or unable’ test. The aim of this article is to show that this test has not been accepted by the international community of states as a whole in the Syrian case. It is also to stress that such an acceptance would lead to a radical transformation of the jus contra bellum regime, one that a large majority of states is probably not ready to accept.