Answer:
In the period of the cold war, the rivalry between the USA and USSR heightened. This rivalry led to the concerns in the US that communists and communist sympathizers in their country were a threat. It was also the period of anti-communist hysteria in the US. The mains reason for this scare was that USSR had used United States citizens as spies. International events such as testing of Nuclear Bomb by USSR, Communist takeover of China. Such events of communist advance caused the fear of communists taking over their country. The outcome of this hysteria was Truman's loyalty program in which Federal employees had to prove their loyalty.