Operation Barbarossa was the code name for Germany's invasion of the Soviet Union during the Second World War. Beginning on 22 June 1941, over 3.9 million troops of the Axis powers invaded the USSR along a 2,900 km (1,800 mi) front, the largest invasion in the history of warfare. In addition to troops, Barbarossa involved 600,000 motor vehicles and 750,000 horses. The ambitious operation, driven by Adolf Hitler's persistent desire to conquer the Russian territories, marked the beginning of the pivotal phase in deciding the victors of the war. The German invasion of the Soviet Union ultimately resulted in 95% of all German Army casualties from 1941 to 1944 and 65% of all Allied military casualties accumulated throughout the war.

Operation Barbarossa was named after Frederick Barbarossa, the medieval German ruler who, as myth had it, would rescue Germany in her time of need. Planning started on 18 December 1940; the secret preparations and the military operation itself lasted from June to December 1941. The Red Army repelled the Wehrmacht's strongest blow, and Adolf Hitler did not achieve the expected victory, but the Soviet Union's situation remained dire. Tactically, the Germans won resounding victories and occupied some of the most important economic areas of the Soviet Union, mainly in Ukraine. Despite these successes, the Germans were pushed back from Moscow and could never again mount a simultaneous offensive along the entire strategic Soviet-German front.