The Vistula–Oder Offensive was a successful Red Army operation on the Eastern Front in the European Theatre of World War II in January 1945. It saw the liberation of Kraków, Warsaw and Poznań. The Red Army had built up their strength around a number of key bridgeheads, with two fronts commanded by Marshal Georgy Zhukov and Marshal Ivan Konev. Against them, the German Army Group A, led by Colonel-General Josef Harpe (soon replaced by Colonel-General Ferdinand Schörner) was outnumbered 5:1. Within days, German commanders evacuated the concentration camps, sending the prisoners on their death marches to the west, where ethnic Germans also started fleeing. In a little over two weeks, the Red Army had advanced 300 miles from the Vistula to the Oder, only 43 miles from Berlin, which was undefend