 In spite of the ambitious standards of accountability for mass atrocity set at Nuremberg and Tokyo, the actual practice of international criminal justice went into a prolonged lull once the Cold War began. The sharp ideological differences between the superpowers made the cosmopolitan ideals underlying such trials less persuasive.  Concerned that war crime prosecutions would become one more arena for political conflict, neither the Americans nor the Russians pursued them. The lull ended with the collapse of the Soviet Union and the end of the Cold War, and the first significant war tribunals thereafter were established by the United Nations in the 1990s—the ad hoc International Criminal Tribunal for the former Yugoslavia at The Hague (ICTY), in 1993, and the ad hoc International Criminal Tribunal for Rwanda in Tanzania (ICTR), in 1995.