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 by Adolf Hitler's ideological desire to destroy the Soviet Union, as outlined in his 1925 manifesto Mein Kampf. In the two years leading up to the invasion, the two countries signed political and economic pacts for strategic purposes. Nevertheless, on 18 December 1940, Hitler authorized an invasion of the Soviet Union, with a planned start date of 15 May 1941. The actual invasion began on 22 June 1941. Over the course of the operation, anywhere between 4-5 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 Germans employed some 600,000 motor vehicles and between 600,000 and 700,000 horses. The offensive marked the beginning of the escalation of the war, both geographically and in the formation of the Allied coalition. Operationally, the Germans achieved surprising victories and occupied some of the most important economic areas of the Soviet Union, mainly in Ukraine, both inflicting and sustaining heavy casualties. Despite their successes, the German offensive stalled on the outskirts of Moscow and was subsequently pushed back by a Soviet counteroffensive. The Red Army repelled the Wehrmacht's strongest blows and forced the unprepared Germans into a war of attrition. The Germans would never again mount a simultaneous offensive along the entire strategic Soviet-Axis front. The failure of the operation drove Hitler to demand further operations inside the USSR of increasingly limited scope, all of which eventually failed, such as Case Blue and Operation Citadel. The failure of Operation Barbarossa was a turning point in the fortunes of the Third Reich. Most importantly, the operation opened up the Eastern Front, to which more forces were committed than in any other theater of war in world history. The Eastern Front became the site of some of the largest battles, most horrific atrocities, and highest casualties for Soviets and Germans alike, all of which influenced the course of both World War II and the subsequent history of the 20th century. The German armies captured 5,000,000 Soviet prisoners of war who were not granted protections stipulated in the Geneva Conventions. A majority of them never returned alive; Germany deliberately starved 3,000,000 of the prisoners to death as part of a "Hunger Plan" that aimed to reduce the population of Eastern Europe and then re-populate it with ethnic Germans. Over a million Soviet Jews were murdered by Einsatzgruppen death squads and gassing as part of the Holocaust.

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