Historians have heatedly debated the Soviet role in the origins of the Second World War for more than 50 years. At the centre of these controversies stands the question of Soviet relations with Nazi Germany and the Stalin-Hitler pact of 1939. Drawing on a wealth of new material from the Soviet Archives, this detailed and original study analyses Moscow's response to the rise of Hitler, explains the origins of the Nazi-Soviet pact, and charts the road to Operation Barbarossa and the disaster of the surprise German attack on the USSR in June 1941.