Lessons of international law from NATO's armed intervention against the federal republic of Yugoslavia

Under the UN Charter, the threat and use of force is prohibited by Article 2.4, which most writers consider a peremptory norm of international law. The use of force by individual states (acting alone or in a military alliance) is permitted only in self-defence under article 51 or against “enemy states”, according to Articles 107 and 53 (the action may be taken by individual states or by a regional organisation). The practice shows that states are lawfully permitted to resort to force, if they are authorised by the UN Security Council (SC), acting under Chapter VII, that is, if the SC determines that there is a threat to peace or a breach of peace or that an act of aggression have taken place. This point is no longer object of controversy, even though writers are questioning whether this permissive rule is the consequence of a custom within the Charter or can simply be derived from Article 48, which states that actions required to carry out decisions of the Security Council for the maintenance of international peace and security shall be taken by all UN members “or by some of them”. 1