Bitter Allies

Humans accusatory instinct is a powerful thing. All humans are given a degree of inward favoritism. Therefore whenever something bad happens, it is natural to blame someone else instead of yourself. That partiality is the driving force behind such episodes in American history as the Salem witch trials (as discussed in the Crucible), the communist hysteria in the 1950s, and the unease of terrorism of modern-day America. In an episode of The Twilight Zone, a neighborhood starts to get suspicious when the power goes out. Everyone suspects their own friends and neighbors as being aliens in human disguise causing all the trouble. In reality the aliens had the last laugh as they were the ones who shut off the power and turned the neighborhood inside out.
Similarly in the Crucible, it is believed that the devils servants are roaming Salem. This hysteria splits-up the closest of relationships.