On August 23, 1939, Nazi Germany and the Soviet Union signed the Molotov-Ribbentrop Pact, affirming a policy of non-aggression between the two countries. In a secret addendum, the two nations also agreed on how they would conquer and divide Poland. The Pact ended when Germany invaded the USSR on June 21, 1941

Learn more about relations between Nazi Germany and the Soviet Union from Yale University.