The Prohibition of the Use of Force

This chapter concerns the central international legal rule against violence: Article 2(4) of the United Nations Charter. Article 2(4) generally prohibits the use of force by states. It is a treaty rule that is also widely regarded as a rule of customary international law and, indeed, in certain respects, as a peremptory rule or rule of jus cogens. Article 2(4) was adopted along with the rest of the Charter in 1945 after the catastrophe of the Second World War in which an estimated 60 million people died. Despite its relatively recent adoption, Article 2(4) has ancient roots, dating back to the emergence of the Just War Doctrine in the fifth century AD and earlier. Moral philosophers, theologians, ethicists and legal scholars held for centuries before 1945 that war is prohibited unless it meets the conditions of the Just War Doctrine. Under the Doctrine war is justified only when fought for certain just causes and then only when the war is a last resort that has a reasonable chance of succeeding. Even when resort to force meets these criteria the cost of achieving success through force must not be disproportionate to the value of the aim in terms of civilian lives lost and property destroyed