The rise of individual criminal responsibility directly under international law marks the coming together of elements of traditional international law with more modern approaches to human rights law and humanitarian law, and involves consideration of domestic as well as international enforcement mechanisms. Although the rights of individuals in international law have evolved significantly in the post-1945 era, the placing of obligations directly upon persons as opposed to states has a distinct, if narrow, pedigree. Those committing piracy or slave trading have long been regarded as guilty of crimes against international society bearing direct responsibility, for which they may be punished by international tribunals or by any state at all. Jurisdiction to hear the offence is not confined to, for example, the state on whose territory the act took place, or the national state of the offender or the victim. This universal jurisdiction over piracy constitutes a long-established principle of the world community. All states may both arrest and punish pirates, provided of course that they have been apprehended on the high seas or within the territory of the state concerned. The punishment of the offenders takes place whatever their nationality and wherever they happened to carry out their criminal activities. Piracy under international law (or piracy jure gentium) must be distinguished from piracy under municipal law. Offences that may be characterised as piratical under municipal laws do not necessarily fall within the definition of piracy in international law, and thus are not susceptible to universal jurisdiction (depending of course upon the content and form of international conventions).
Piracy jure gentium was defined in article 15 of the High Seas Convention, 1958 (and reaffirmed in article 101 of the 1982 Convention on the Law of the Sea) as illegal acts of violence, detention or depredation committed for private ends by the crew or passengers of a private ship or private aircraft and directed against another ship or aircraft (or persons or property therein) on the high seas or terra nullius. Attempts to commit such acts are sufficient to constitute piracy and it is not essential for the attempt to have been successful.
However, the range of offences under international law for which individuals bore international responsibility was narrow indeed. It is doubtful whether it had extended beyond piracy and slave trading by the turn of the twentieth century.