The rules governing the use of force in the international system were primarily designed with respect to armed conflict between states. As will be shown, some consideration was given at an early stage to the subject of attacks on a state by ‘armed bands’ or what we could call today in a formal sense – non-state actors – or, more politically, ‘terrorists’. Yet, this was never a major focus. Increasingly since 1945 and, especially, since 2001, rules governing a state’s rights in countering terrorism have moved to a central place in international affairs (Pilgrim 1990: 173-74).