On August 23, 1939, the Treaty of Non-aggression between Germany and the Union of Soviet Socialist Republics, known as the Molotov-Ribbentrop Pact, is sign between Nazi Germany and the Soviet Union. Named after German foreign minister Joachim von Ribbentrop and his Soviet counterpart Vyacheslav Molotov, the treaty saw both countries agree to neither aid nor ally with an enemy of the other. Furthermore, both parties agreed to certain spheres of influence in Eastern Europe, including plans for dividing territories such countries as Poland, Finland, and the Baltic states. As a result of the agreement, German and Soviet forces would invade Poland in September, leading to the beginnings of the Holocaust in Poland as well as the Soviet-perpetrated Katyn Massacre. The Soviet Union would also go on to invade Finland in the Winter War and annex Latvia, Lithuania, and Estonia. Furthermore, Romania soon lost large portions of its territory to the Soviet Union and German-backed neighboring states.

The Molotov-Ribbentrop Pact was ultimately rendered void on June 22, 1941, when Germany launched a massive invasion of the Soviet Union and Soviet-controlled territories with Operation Barbarossa. The Soviet Union had lost all territory which it had gained through the pact in a matter of weeks. Over the following four years, the two countries would suffer tens of millions of casualties, finally ending with the collapse of Nazi Germany in 1945 and Soviet domination of Eastern Europe until the 1980s and 90s.

Joachim von Ribbentrop was found guilty on charges of crimes against peace, deliberately planning a war of aggression, war crimes, and crimes against humanity at the Nuremberg Trials. He was sentenced to death and executed by hanging on October 16, 1946. Vyacheslav Molotov was replaced as Foreign Minister in 1949 and had fallen out of favor with Stalin; however, he would regain his position following Stalin's death in 1953. He would again lose his position in 1956 after a failed attempt to oust Khrushchev. Molotov was later expelled from the Communist Party and removed of all government positions during Khrushchev's de-Stalinization. Vyacheslav Molotov passed away on November 8, 1986, while in hospital.