The fear of communism really started after the Soviet Union emerged as a global superpower after World War II. The United States was worried that this system would spread throughout Europe, limiting America's influence and the rights of citizens all over the world.
Some of the key figures in the second Red Scare are Joseph McCarthy and Richard Nixon. McCarthy was the ring leader of the hunt for communists. This became known as McCarthyism. This lead an increased amount of individuals being called in front of Congress in the House Un-American Activities Committee. This resulted in the arrest of several innocent American citizens and resulted in the blacklisting of several Hollywood producers and actors.