In 1949, the Soviet Union detonated its first atomic device, ending the United States' short reign as the sole atomic power on Earth. The entry of the Soviets into the atomic club made Americans nervous, not to mention a little suspicious: how did the USSR get the bomb so fast?
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When it came to light that Soviet spies in the US atomic program had passed secrets to Russia, Americans began to worry that spies might be lurking in every corner of society. In the late 1940s and early 1950s, there were several highly-publicized espionage trials that convicted leading scientists and government figures of espionage, culminating in the 1953 execution of scientist Julius Rosenberg and his wife Ethel for passing information about the atomic bomb to Russia. These convictions served to justify fears that spies could be active throughout the country.
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