Most historians concur that Hitler’s decision to invade the Soviet Union was one of the primary causes of Germany’s ultimate defeat. By invading the USSR, Germany made essentially the same mistake that Japan made by expanding so far across the Pacific. The huge expanse of the Soviet Union and the vast distances between its major cities required an enormous German invasion force. Despite this geographical challenge, Hitler assumed that Operation Barbarossa would take only six months, expecting Russia to capitulate rapidly after the shock of Germany’s initial, devastating attack. When events transpired differently, the German forces were faced with an enormous challenge, as their forces were dispersed and poorly equipped to deal with the brutal Russian winter. Russian soldiers and civilians, conversely, had plenty of room to retreat east when necessary, which caused the pursuing Germans to extend their supply lines so far that they were unable to maintain them. It was under these conditions that the Germans had to fight the massive battles of Stalingrad and Kursk. After the Germans lost both of these battles, they were no longer capable of maintaining their position and were forced to retreat to the west. Within a matter of months, the pursuing Red Army had pushed the Germans back through eastern Europe and toward a last stand on their home turf, which was the beginning of the end of the Nazi empire.