What was the name given to the widespread fear of suspected communists and radicals in the united state after world war 1 ?

A. The Red Scare

Communists were associated with the color red because of the red flag of the Soviet Union -- thus the "Red Scare." One manifestation of the Red Scare was how people's privacy was invaded. Accusations about communists and communist sympathizers were aimed at all sorts of people.  Many people in the Hollywood film industry were targeted during that time, for instance.  But defenders of freedom (including film and television people) fought back against that.  Those who aimed to protect the rights and liberties of each individual saw the Red Scare tactics as "witch hunts," where we suspect our neighbors of evil for no good reason.

Speaking of "witch hunts," the playwright Arthur Miller wrote a really powerful play in 1953, during the Cold War, which focused on the Salem witch trials. He was making the point that what was happening in the Red Scare (hunting for communists) was another manifestation of the witch-burning craze that had happened at a previous time in history.