Black cats have consistently played an important role in folklore and superstition throughout history.
In the Middle Ages, black cats were believed to be the evil, supernatural servant of witches, sent by the devil himself. They were also thought to be witches who transformed into the nocturnal, stealthy creatures for optimal witchcraft.
These beliefs led to the widespread eradication of black cats in Europe, which ultimately led to the outbreak of the Bubonic Plague (because the cats ate the rats that carried the plague).
Religious groups eventually brought the persecution of witches and black cats with them when they immigrated to America. The Salem witch trials of 1692 saw the persecution of many suspected witches and black cats, cementing the superstition into American history. Because of their history, black cats are now commonly used around Halloween to enhance the fear factor of the holiday.