1939–1941

Contrary to the impression Soviet diplomats wanted to create, the Molotov-Ribbentrop pact was more than a nonaggression treaty; Germany and the Soviet Union became de facto allies. A secret protocol was attached to the pact that delimited the future “spheres of influence” of the contracting parties, according to which the Soviet Union was to have a free hand in Finland, Bessarabia, Latvia, and Estonia. The protocol also established the precise line in Poland that was to divide German and Soviet occupation spheres. At the end of September, Ribbentrop returned to Moscow to modify the original division: Lithuania now fell in the Soviet zone, but the Wehrmacht occupied the Lublin district in Poland. Remarkably, as long as the Soviet Union lasted, Soviet spokesmen and historians denied that there was such a protocol despite all the available evidence.

Stalin concluded his pact with the Nazis because he believed that the British and French would live up to their commitment to Poland and embark on a large-scale European war that would tie down Germany for some time. Without such a war, German military presence at the newly drawn Soviet border was too frightening to contemplate. Indeed, the Western powers declared war on Germany on September 3, and the Second World War began. The Soviet Union resisted German pressure and waited until September 17, that is until the Polish forces were more or less destroyed, before the Red Army crossed the Polish border and came to occupy territories assigned to it.