Most states regulated the behaviour of combatant troops in operation well before the First World War, with laws applicable to the armed forces grouped in codes which condemned forms of conduct considered undesirable. The determination to suppress violence as the way to settle differences between nations is the ultimate aim of the laws of war. This concept must be retained in any analysis of the evolution of international law, through a mixture of idealism and pragmatism. This pacifist aim is anchored in two lines of approach which are not mutually exclusive. The first approach can be defined as compassionate because it arises from sensitivity to the sufferings caused by wars. The second approach, the rationalist approach, arose from consideration of the cost of modern warfare in terms of lives and destruction, lessons learned from the wars of the second half of the nineteenth century.