With help from their Soviet allies, the Partisans (by then recognized as the Yugoslav army), joined by Bulgarian and Italian forces, fought a difficult winter campaign and finally broke through the front on 12 April 1945.

From September 1944 to January 1945, Army Group E pushed its way through Macedonia, Kosovo, Sanjak, and Bosnia, and soon their sole available escape route was in a line between Sarajevo and Slavonski Brod.

To prevent Army Group E from being cut off, the German South-East command prepared seven successive fortified defense lines between the Danube and Sava river from Ruma to Vinkovci.

[5] Young men from Vojvodina and Central Serbia, many from freshly liberated regions, were drafted en masse and sent to the front, and the amount of training they received and their casualty levels remain in dispute.

The Yugoslav First Army, commanded by Peko Dapčević, broke through German XXXIV Corps defenses in Syrmia on 12 April, quickly capturing the cities of Vukovar, Vinkovci, and Županja, and enabling further advances through Slavonia toward Slavonski Brod and Zagreb in the last month of the war.