Operation Barbarossa (German: Unternehmen Barbarossa ) was the code name for Nazi Germany 's World War II invasion of the Soviet Union , which was launched on 22 June 1941. The operation was driven primarily by an ideological desire to conquer the Western Soviet Union so that it could be repopulated by Germans. In the two years leading up to the invasion, the two countries signed political and economic pacts for strategic purposes. Nevertheless, the German High Command began planning an invasion of the Soviet Union in July 1940 (under the codename Operation Otto ), which Hitler authorized on 18 December 1940. Over the course of the operation, about four million Axis personnel invaded the western Soviet Union along a 2,900-kilometer (1,800 mi) front, the largest invasion force in the history of warfare. In addition to troops, the Wehrmacht employed some 600,000 motor vehicles and between 600,000 and 700,000 horses....