The Soviet Union played a crucial role in World War II, initially allying with Nazi Germany through the Molotov-Ribbentrop Pact but becoming a primary combatant against the Nazis following Operation Barbarossa in 1941. The USSR endured immense casualties and destruction, with significant battles like Stalingrad turning the tide in favor of the Allies. Under Joseph Stalin's leadership, the Red Army pushed German forces back, eventually capturing Berlin in 1945. Despite the victory, the USSR suffered enormous losses, emerging as a superpower with deep scars from the conflict.