The Cold War began in 1945 after World War 2 and lasted until 1989. It was a period of geopolitical tension between the Soviet-led Eastern Bloc and the US-led Western Bloc due to their opposing ideologies of communism and capitalism. This divide threatened nuclear war as both sides developed powerful weapons, especially nuclear bombs. Underlying causes included tensions between the US and USSR dating back to the 1917 Russian Revolution, as well as disagreements over postwar control of countries like Germany and crises like the Korean War.