11. Use of force

Abstract

This chapter examines under what circumstances States may use armed force under customary international law and Arts 2(4) and 51 UN Charter. After noting that the use of armed force is generally prohibited and only limited to self-defence, and then only if the target State is under an armed attack, we show that several States have expanded the notion of armed attack. Besides self-defence, the United Nations Security Council may authorize the use of armed force through a process of collective security. Several examples of collective security are offered, as well as the ICJ’s position on what constitutes an armed attack. In recent years, the range of actors capable of undertaking an armed attack has included terrorists. Moreover, the development of the doctrine of the responsibility to protect is a significant achievement.