Why did the nuclear arms race begin in 1949?

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.

Explanation:

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the deaths of over a million communist soldiers

post-traumatic stress disorder in veterans