The Cold War was a period of tension and rivalry between the United States and the Soviet Union from 1945-1990. The two superpowers had opposing ideologies of capitalism/democracy versus communism/socialism and were in an arms race to develop powerful nuclear weapons. This led to several proxy wars like the Korean War and Vietnam War as the sides tried to prevent the spread of the other's influence. Crises like the Berlin Blockade and Cuban Missile Crisis brought the world close to nuclear war. The Cold War ended in the late 1980s as reformist leader Gorbachev took power in the USSR and liberalized policies, eventually leading to the dissolution of the Soviet Union in 1991.