What caused the us to go through the red scare in the 1920's? ?

As the Cold War between the Soviet Union and the United States intensified in the late 1940s and early 1950s, hysteria over the perceived threat posed by Communists in the U.S. became known as the Red Scare. (Communists were often referred to as “Reds” for their allegiance to the red Soviet flag.) The Red Scare led to a range of actions that had a profound and enduring effect on U.S. government and society. Federal employees were analyzed to determine whether they were sufficiently loyal to the government, and the House Un-American Activities Committee, as well as U.S. Senator Joseph R. McCarthy, investigated allegations of subversive elements in the government and the Hollywood film industry. The climate of fear and repression linked to the Red Scare finally began to ease by the late 1950s.