Arms race
Not long after World War II ended in 1945, new hostilities emerged between the United States and the Soviet Union. Known as the Cold War, this conflict began as a struggle for control over the conquered areas of Eastern Europe in the late 1940s and continued into the early 1990s. Initially, only the United States possessed atomic weapons, but in 1949 the Soviet Union exploded an atomic bomb and the arms race began. Both countries continued building more and bigger bombs. In 1952, the United States tested a new and more powerful weapon: the hydrogen bomb. The Soviet Union followed with its own version in 1953.