In 1949, the Soviet Union detonated their first atomic bomb, many years before anyone in the United States had expected them to accomplish this feat. Also in 1949, Klaus Fuchs was arrested in Great Britain for espionage. He subsequently confessed to giving the Soviets the secrets of the atomic bomb during his years of work at Los Alamos. After World War II, Russian troops remained in the Eastern European countries of Albania, Bulgaria, Czechoslovakia, Hungary, Romania, and Yugoslavia, effectively making them Russian satellites. The Soviets cut off all contact with the Western democracies. The Soviet "Iron Curtain" descended across Eastern Europe. The dream of international control of nuclear weapons was dead and the Cold War era had begun.

The United States began developing an even more powerful nuclear weapon to counter any potential Soviet threat. The first American hydrogen bomb was tested in...