What did Americans fear during the red Scare?

During the Red Scare, the Americans feared the spread of communism (red was the colour of the flag of the communist Soviet Union and the communist emblem known as the red star).

There were two Red Scares in U.S.A.:

1) 1919-1920: Fear of socialist revolution and political radicalism (red is a symbol of radical ideology).

2) 1947-1957: Fear of national and foreign communism influencing American society and/or infiltrating the federal government.