Miller's play isn't directly about Communists, but witches were the Communists of the 17th century. This isn't to say Communists were laying the evil eye on anybody, but it's the same sort of thing: a permeating terror of an unseen foe who infiltrates every corner of life for some nefarious purpose.

The Crucible is an allegory, a story where one thing is used to represent another thing in order to, you know, make a point. Arthur Miller wrote The Crucible in 1953, which was the darkest year of the McCarthy Era. Now we know that McCarthy was about to get the smackdown, but Miller couldn't have known that.

In this play, Miller uses the literal witch hunt in colonial Salem, Massachusetts as a stand-in for the figurative witch hunt for Communists presently claiming the lives and careers of his friends. Even writing this play was an act of courage; Miller could very easily have been painted with the same fear-mongering brush and been humiliated and ostracized.

Instead, he got a Tony.

He got Marilyn Monroe, too, but that's another story.