However, some German historians claim that after 1939 Poland did not exist, and the execution of Polish law on German-held territory was therefore against international law. These claims remain controversial, since the annexation of Poland in 1939 was unilateral and acknowledged only by the Axis Powers and the USSR (which later declared its pact with Germany null and void). Moreover, the invasion was itself in violation of international law (German officials were later prosecuted at the Nuremberg Trials for it), being an act of aggression (despite a German false flag attack that sought to show Polish provocation).