The operation opened up the Eastern Front, in which more forces were committed than in any other theater of war in history. The offensive marked a massive escalation of World War II, both geographically and in the formation of the Allied coalition including the Soviet Union. Over the course of the operation, over 3.8 million personnel of the Axis powers-the largest invasion force in the history of warfare-invaded the western Soviet Union along a 2,900-kilometer (1,800В mi) front, with 600,000 motor vehicles and over 600,000 horses for non-combat operations. Following the Soviet occupation of Bessarabia and Northern Bukovina, the German High Command began planning an invasion of the Soviet Union in July 1940 (under the codename Operation Otto).

In the two years leading up to the invasion, Germany and the Soviet Union signed political and economic pacts for strategic purposes. Their ultimate goal was to create more Lebensraum (living space) for Germany, and the eventual extermination of the indigenous Slavic peoples by mass deportation to Siberia, Germanisation, enslavement, and genocide. The German Generalplan Ost aimed to use some of the conquered people as forced labour for the Axis war effort while acquiring the oil reserves of the Caucasus as well as the agricultural resources of various Soviet territories. The operation, code-named after Frederick Barbarossa ('red beard'), a 12th-century Holy Roman emperor and German king, put into action Nazi Germany's ideological goal of conquering the western Soviet Union to repopulate it with Germans.

Operation Barbarossa (German: Aktion Barbarossa) (Russian: РћРїРµСЂР°С†РёСЏ Р‘Р°СЂР±Р°СЂРѕСЃСЃР°) was the invasion of the Soviet Union by Nazi Germany and most of its Axis allies, starting on Sunday, 22 June 1941, during World War II.

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