Geneva Conventions as Customary Law
The few international judicial decisions on international humanitarian law reveal little, if any, inquiry into the process by which particular instruments have been transformed into customary law. The leading case on the Hague Regulations of 1907 is the judgment of the International Military Tribunal (IMT) for the Trial of German Major War Criminals ( Nuremberg, 1946). The argument was raised that Hague Convention No. IV did not apply because of the general participation (si omnes) clause -- several of the belligerents not being parties to the Convention. In response, the IMT apparently acknowledged that at the time the Regulations were adopted the participating states believed that they were making new law: '[b]ut by 1939 these rules laid down in the Convention were recognised by all civilised nations, and were regarded as being declaratory of the laws and customs of war'.1 The IMT did not even discuss the process by which the Hague Regulations had metamorphosed from conventional into customary law. The Tribunal's language (the use of the word 'regarded') suggests that the Tribunal may have looked primarily at the opinio juris, rather than at the actual practice of states.
Similarly, although more cautiously, the International Military Tribunal for the Far East ( 1948) characterized Hague Convention No. IV 'as good evidence of the customary law of nations, to be considered by the Tribunal along with all other available evidence in determining the customary law to be applied in any given situation'.2 This Tribunal, in contrast to the IMT, did not view the entirety of the Hague Regulations as necessarily an accurate mirror of customary law.
The most interesting case on the relationship between custom and treaty in the context of the Geneva Conventions is United States v. von Leeb ('The High Command Case').3 The IMT judgment focused on the____________________