Unlike most other areas of international law which address only State responsibilities, the law of war assigns to individuals the responsibility to observe positive rules. The threat of being charged with a war crime, with all the attached opprobrium, is the chief means by which observance of the law of war is ensured. No one could rightly argue that war crimes prosecutions, even if they were always effectively prosecuted – and they are not – ensure perfect compliance with the law, but they are the best mechanism devised to date. Although war crimes trials has earlier antecedents, the prosecutions following World War II marked the beginning of the modern war crimes model.
World War II prosecutions were notable for the scale of atrocities alleged in the various indictments. Once the crimes were defined, and the architecture put in place to establish the various tribunals, proof of wrongdoing was rarely in doubt. There were expected legal issues to be sure: claims of ex post facto crimes, immunities for acts of state, and the defense of superior orders, among many others; but in general prosecutors fully expected convictions across the board. And many convictions did result, though there were several exceptions that resulted in full or partial acquittals.