The Cold War developed between the United States and Soviet Union following World War II as tensions grew over differing ideologies and Soviet expansion into Eastern Europe. This led to an arms race, proxy wars like Korea and Vietnam, and space race as each side sought to contain the influence of the other. Key events included the Berlin Blockade, formation of NATO and Warsaw Pact alliances, and Cuban Missile Crisis bringing the world close to nuclear war. The Soviet Union collapsed in 1991, ending the Cold War.