what event led to the soviet union joining the side of the allies during World War II

The United States successfully defeated the Soviet during operation barbarossa

Germany broke the German Soviet non-aggression pact

The Soviets and Italians wanted to join forces to defeat, Germany

Japan and Germany secretly agree to invade the Soviet union

Germany breaking the German-Soviet non-aggression pact led to the Soviet Union joining the side of the Allies during World War II.