What were all Americans afraid of during the red scar

They were scared of the communist. I dont remember who said it but he said he had a list of Government workers who where really Communist. So that scared Americans. But to answer your question. It was Communist

In the Red Scare in 1950s, the Americans were afraid of the communists in America. The fear of the communists in the America caused hysteria in the society that was referred to as the Red Scare caused by the cold war between U. S. and Soviet Union.