Joseph Stalin controlled the foreign policy of the Soviet Union , with Vyacheslav Molotov as his foreign minister . Their policy was neutrality until August 1939 . The Soviet military had conversations in Moscow with a high level military delegation from Britain and France . The Soviets demanded an agreement from Poland to allow Soviet troops to enter that country to defend it against Germany , but Poland refused . Those talks went nowhere . On August 21 , Hitler made friendly proposals to Stalin that led to the Molotov – Ribbentrop nonaggression pact on August 23 that stunned the world . The Soviets achieved friendly relations with Germany in order to carve up Key elements of Eastern Europe , especially Poland and the Baltic states . Following the pact , Germany invaded and quickly defeated Poland ; then the Soviets invaded and took control of its preassigned areas of eastern Poland . Both invaders systematically decimated the Polish elite . In the 1940 Katyn massacre , the NKVD ( Soviet secret police ) executed 22,000 Polish military and police officers and civilian intelligentsia
Katyn massacre
Katyn massacre
Diplomatic history of World War II