Operation Barbarossa was the invasion of the Soviet Union by Nazi Germany and many of its Axis allies, starting on Sunday, 22 June 1941, during the Second World War. It was the largest and costliest land offensive in human history, with around 10 million combatants taking part, and over 8 million casualties by the end of the operation.

After the Nazis rose to power in Germany in 1933, relations between Nazi Germany and the Soviet Union began to deteriorate rapidly. Trade between the two sides decreased. Following several years of high tension and rivalry, the two governments began to improve relations in 1939. In August of that year, the countries expanded their economic relationship by entering into a Trade and Credit agreement whereby the Soviet Union sent critical raw materials to Germany in exchange for weapons, military technology and civilian machinery. That deal accompanied the Molotov–Ribbentrop Pact, which contained secret protocols dividing central Europe between them, after which both Nazi forces and Soviet forces invaded territories listed within their "spheres of influence".