Abstract

This essay argues that in Resolution 2249 (2015) the UN Security Council calls upon Member States to adopt 'all necessary measures' against ISIS - also with regard to the use of force - already "lawful" under international law. The use of force, however, can be justified on legal arguments which are different from those referred to by the US-led coalition, in particular self-defence according to Article 51 of the UN Charter. As for the military intervention in Iraq, the legality of the use of force seems to rest on the consent of the Iraqi government and its explicit request of assistance to the international community in deterring the ISIS threat in its territory. As to the use of force in Syria, it can be argued that its legality rests upon the consent of the whole international community to repel the global and common threat represented by ISIS, and absent any objection to the legality of the military intervention by the generality of States.