With the onset of World War II, the Hungarian-Serb relations were low. Nazi Germany, in accordance to its "Operation Punishment" plan, invaded Yugoslavia, and subsequently, Axis Hungarian forces occupied Bačka. Hungary annexed this region, and it was settled by new Hungarian settlers, at which time the number of Hungarians in the area grew considerably. In contrast, at the same time, many Serbs were expelled from Bačka. The brutal conduct of the Axis Hungarian occupying forces, including the Hungarian army and , has polarized both Hungarian and Serb communities. Under the Axis Hungarian authority, 19,573 people were killed in Bačka, of which the majority of victims were of Serb, Jewish and Romani origin.