The Cold War Era lasted from 1947-1970 and marked a period of geopolitical tension between the Western Bloc led by the United States and its NATO allies, and the Eastern Bloc led by the Soviet Union and its Warsaw Pact allies. Key events that heightened tensions included the Soviet Union developing nuclear weapons in 1949, creating an arms race, and the Cuban Missile Crisis of 1962 bringing the US and USSR to the brink of nuclear war. The world divided into two power blocs with countries joining either NATO or the Warsaw Pact, while some non-aligned nations formed the Non-Aligned Movement to stay out of the Cold War alliances.