International criminal law is a new branch of law, with one foot in international law and the other in criminal law. Until the Nuremberg trial, international criminal law was largely ‘horizontal’ in its operation – that is, it consisted mainly of co-operation between states in the suppression of national crime. Extradition was therefore the central feature of international criminal law. Of course there were international crimes, crimes that threatened the international order, such as piracy and slave trading, but with no international court to prosecute such crimes, they inevitably played an insignificant part in international criminal law
