The Cold War
World War II had ended, but by 1948, tensions between the U.S. and Soviet Union began to build. In June 1950, with support from the Soviets, North Korea invaded South Korea, leading to the start of the Korean War. The United States, believing the conflict signaled the start of communism spreading across the world, intervened. America used a containment strategy for dealing with the Soviet Union: Be patient and watch Russia to prevent its expansion of communism.
The U.S. strategy of containment set the stage for a deadly arms race with the Soviets. As the United States was developing more atomic weapons, the Soviets also were testing their own. Both countries continued developing increasingly destructive weapons, eventually leading to the development of the hydrogen bomb.