What is the crucible about?
The Crucible is a play by Arthur Miller written in the 1950s about the Salem Witch Trials of 1692. He used primary source documents and real names to play out for viewers on a stage these violent killings.
Here's the jist. A group of girls with their ringleader Abigail acted like typical teenagers... they lied to get their way, but they went a little too far. They accused any adults in the town with whom they disagreed of being witches. A great body of government actual heard these girls cries and considered their spectral evidence as truth and actually hung 19 good and moral people who were not witches, only accused.
The reason this story was so important in the 50s, and the reason you are talking about it in history is because a Senator McCarthy was having an issue with communist sympathizers. We were at the height of the Cold War as a nation and people did assume the Communist Soviet Union would have spies all over the place. McCarthy went on a 'witch-hunt' hoping to point out all these dissenters. This didn't go to the extreme of hangings, but the story of The Crucible put his actions in plain view for people to see. Many believe Miller's work to be an allegory of McCarthy's actions.
The Crucible is an allegory, a narrative where characters, their actions, and the setting are all symbolic of abstract ideas or issues. Certainly, Arthur Miller reflects on the paranoia of McCarthyism in this play. But another view to take might be to look at the qualities of human nature symbolized by the characters. For example, Thomas Putnam could represent "greed" because everything he does is motivated by greed. Parris might, in this realm, symbolize "hypocrisy," and Abigail "lust." Pit those characters against Giles Corey who could represent "integrity," Rev. Hale who could represent "mercy," and Elizabeth who might symbolize "conscience." Thus, you have a work that not only brings out the paranoia of McCarthyism and the evils of Puritan theocracy, you have a more general allegory about conflicts in human nature.
The previous responses have discussed the problem area quite well. If I could suggest one other interpretation it would be that Miller's work is about how individuals withstand social pressure. One of the most overwhelming elements of the play is how individuals react to social pressure. The requirement of courage and independence of thought in the midst of collective perception is a theme explored in the play. The idea of individuals having to remain silent in order to maintain their own sense of perception in the eyes of others, the manipulation of truth, and the pain needed to defend one's name in a setting where inverted values of justice and honesty have become apparent are also thematic elements which guide Miller's work.
The play "The Crucible" is a play that relates to the witch trials in Salem and the consequences that can occur when people go off on a superstitious tangent.
John Proctor has an affair with a hired girl named Abigail. He feels guilty so he tells his wife that he is thinking about the girl inappropriately. Elizabeth (Goody) Proctor sends the girl away. Later she is told by John that he actually had a relationship with the girl.
Abigail becomes the center of the town when she begins to state she is seeing people perform bewitching things to her. Her female friends go along with her. The situation becomes so severe that the townspeople call for an expert to come in and make sure if al the people who have been arrested are really guilty of engaging in the supernatural. Reverend Hale comes to the town.
A series of interrogations occurs. Abigail wanting Proctor and angered at his rejection lies about his wife saying Goody Proctor has done something to her by using a doll. Elizabeth is charged with witchcraft. In addition, the frenzy gets so crazy that who ever someone does not like, they are accused of witchcraft.
John Proctor feels terrible guilt for his wife's situation and tries to tell the truth, but he is not believed. However, the Reverend believes that the people are innocent and tries to convince Danforth. Danforth refuses to believe him. People who are innocent die because of false accusations.