1. From 1899 to the Second World War

The 1899 and 1907 Hague Conventions on Land War, and the Regulations annexed to them, are vague on the matter of ensuring compliance. Article 1 of the 1899 and 1907 Hague Conventions requires the powers to issue instructions to their land forces in conformity with the Regulations. Article 3 of the 1907 Convention says that a belligerent party violating the Regulations "shall, if the case demands, be liable to pay compensation". In addition, Article 56 of the 1899 and 1907 Hague Regulations makes a vague reference to legal proceedings in the event of violation of its rules about certain types of public property. Nothing more is said about how these or other provisions are to be enforced. The many striking omissions regarding enforcement exposed the Hague system to the accusation that it was based on unduly optimistic assumptions.

However, the relative paucity of formal provisions in the Hague Conventions and Regulations did not mean that there was no implementation system at all. The central assumption, of which the above-summarized provisions are a mere reflection, was of a responsibility on states to ensure that the rules were observed and offenders brought to justice. This assumption has many weaknesses, of which the most obvious, easy to identify but hard to remedy, is that most governments have been, quite understandably, reluctant to prosecute their own servants in cases where their violations of the laws of war were carried out while pursuing government policy. It is this problem above all which has sustained an unbroken series of calls for some diminution of national sovereignty so far as the punishment of war crimes and crimes against humanity is concerned. In twentieth century practice, the Hague Regulations have provided the basis for numerous trials, appeals, arbitrations, and inquiries - not only by national, but also by international, bodies. Their modes of implementation have been richer than those specified in the original texts.

After the First World War a number of international agreements included reference to the punishment of war crimes. The 1919 Treaty of Versailles, Articles 227 to 230, required Germany to surrender for trial members of its armed forces charged with violations of the laws of war. However, by subsequent arrangement with Allied governments, Germany itself tried German offenders, very few of whom were convicted The Versailles Treaty also imposed heavy reparations on Germany on account of its perceived responsibility for the outbreak and therefore the costs of the war - a matter of ius ad bellum rather that ius in bello. The 1929 Geneva Convention on Wounded and Sick, Article 29, provided for punishment of violations on the basis of national penal legislation. The 1929 Geneva Convention on Prisoners of War, Article 86, provided for Protecting Powers to monitor observance of the Convention. both these 1929 Conventions are now defunct, having been superseded by the 1949 Conventions.)

By contrast, a major laws of war agreement of the inter-war years, the 1925 Geneva Protocol of Gas and Bacteriological Warfare, said nothing about implementation other than in the noble but vague formulation "that this prohibition shall be universally accepted as a part of International Law, binding alike the conscience and the practice of nations" On ratification, France and many other states remedied the gap by making it clear that they would cease to be bound by the Protocol if their enemies used the prohibited weapons. Here was a clear threat of reprisals. Fear of reprisals almost certainly played some part in subsequent cases of non-use of such weapons, including during the Second World War and the 1991 Gulf War.