The Independent State of Croatia was founded on 10 April 1941, with the full support of Nazi Germany and Fascist Italy. During the four years of its existence, the Independent State of Croatia was ruled by the Ustasha movement and its leader (Poglavnik), Ante Pavelić, who had made plans for the extermination of the Serbs while still an émigré. On 7 June 1941, on the occasion of Pavelić’s first visit to Hitler, the Ustasha movement gained the full support of Nazi Germany for carrying out genocidal policies aimed at the Serbian population. At a meeting with the German ambassador in Zagreb on 4 June 1941, it was concluded that the Serbian question could be resolved by the mass removal of Serbs to Serbia, mass executions in the field, and deportations to concentration camps. The Government of the Independent State of Croatia, at their own request, were included in the transfer plan, and promised to deport to Serbia 30,000 more Serbs than the number of Slovenes who would be transferred to Croatia from the Third Reich.

Since the coming to power of the Ustasha movement had been entirely dependent on the policies of the Third Reich and, initially, of Fascist Italy, Pavelić and his closest colleagues were under the domination and complete influence of these states. This was clearly reflected in the setting of state borders.

A large part of the Croatian coastline, Gorski Kotar and part of Dalmatia (from Zadar to Split), the eastern part of Konavle and Boka Kotora, and almost all the islands (except Brač, Hvar and Pag) were annexed to Italy. Horty’s Hungary annexed Međimurje in December 1941. The remaining parts of Croatia, the territory of Bosnia and Herzegovina and the Srijem region formed the territory of the Independent State of Croatia.

There was a population of about 6,640,000 living in an area of 102,725 km², including Croats, Serbs, Jews, Germans, Hungarians, Roma, Czechs, Ruthenians, Slovenes, Slovaks, Ukrainians, and others.