During World War II, the Kingdom of Hungary engaged in the military occupation, then annexation, of the Bačka, Baranja, Međimurje and Prekmurje regions of the Kingdom of Yugoslavia. These territories had all been under Hungarian rule prior to 1920, and had been transferred to Yugoslavia as part of the post-World War I Treaty of Trianon. They now form part of several states: Yugoslav Bačka is now part of Vojvodina, an autonomous province of Serbia, Yugoslav Baranja and Međimurje are part of modern-day Croatia, and Yugoslav Prekmurje is part of modern-day Slovenia. The occupation began on 11 April 1941 when 80,000 Hungarian troops crossed the Yugoslav border in support of the German-led Axis invasion of Yugoslavia that had commenced five days earlier. There was some resistance to the Hungari