The Warsaw Uprising was a major World War II operation, in the summer of 1944, by the Polish underground resistance, led by the Home Army, to liberate Warsaw from German occupation. The uprising was timed to coincide with the retreat of the German forces from Poland ahead of the Soviet advance. While approaching the eastern suburbs of the city, the Red Army temporarily halted combat operations, enabling the Germans to regroup and defeat the Polish resistance and to raze the city in reprisal. The Uprising was fought for 63 days with little outside support. It was the single largest military effort taken by any European resistance movement during World War II.