Delegates from fifty nations attended the first meeting of the United Nations, held in April 1945 in San Francisco. The goal of the UN was to work toward world peace. A Cold War developed between the United States and the Communist government of the Soviet Union. The United States and Western European countries formed the North Atlantic Treaty Organization (NATO) to prevent the spread of communism.

President Truman created the Marshall Plan to help Western Europe rebuild after World War II. In the 1950s, the Korean War began, the United States competed with the Soviet Union in the arms race and the space race, and Senator Joseph McCarthy formed a committee that falsely accused many people of being communists. In 1953, Dwight D. Eisenhower became President. The economy was prospering and many Americans were able to buy their own homes, television sets, and household appliances.

When John F. Kennedy became President in 1960, he faced major problems in Berlin and Cuba. After World War II, the eastern part of Berlin was occupied by the Soviets and the western part of France, Britain, and the United States. In 1961, the East Germans built the Berlin Wall to stop people from fleeing into West Germany. Fidel Castro took power of Cuba in 1959 and established a Communist government, receiving aid from the Soviet Union. In 1961, the United States supported an unsuccessful attempt to invade Cuba, and in 1962, the United States discovered the Soviets installing missiles there. Kennedy ordered the Navy to blockade Cuba and the Soviets stopped sending missiles. This became known as the Cuban Missile Crisis.