In April 1941, Yugoslavia was occupied by Nazi Germany and Fascist Italy. Following the invasion, most of Croatia, Bosnia and Herzegovina, and the region of Syrmia were incorporated into the Independent State of Croatia (NDH), a Nazi-backed puppet state. Parts of Dalmatia were annexed by Italy and the northern Croatian regions of Baranja and Međimurje by Hungary. The NDH regime was led by Ante Pavelić and ultranationalist Ustaše, a fringe movement in pre-war Croatia. With German and Italian military and political support, the regime introduced racial laws and enacted a genocide campaign against Serbs, Jews, and Roma. Many were imprisoned in concentration camps, the largest of which was the Jasenovac complex. Anti-fascist Croats were targeted by the regime as well. Several concentration camps were also established in Italian-occupied territories, mostly for Slovenes and Croats. At the same time, the Yugoslav Royalist and Serbian nationalist Chetniks pursued a genocidal campaign against Croats and Muslims, aided by fascist Italy.