Answer:
The Cold War began after World War II when the Soviet Union and the United States emerged as superpowers with different ideologies. The United States believed in capitalism and democracy, while the Soviet Union was a communist state. The two nations had been allies during World War II, but their relationship quickly deteriorated. The Soviet Union was expanding its sphere of influence in Eastern Europe, while the United States was working to contain communism. This led to a series of proxy wars, including the Korean War and the Vietnam War. Both sides engaged in a nuclear arms race, with the Soviet Union testing its first atomic bomb in 1949. The U.S. responded by developing the hydrogen bomb. The Cold War lasted until 1991 when the Soviet Union collapsed.