According to the ASPCA, the ancestors of pit bulls are from England. They were likely a breed of bulldog but are not related to the English bulldog, which is a much younger breed.
The term pit bull does not refer to a single breed of dog but possibly two and as many as five. The two breeds unanimously accepted by dog experts are the American Bull Terrier and the American Staffordshire Terrier. Pit bulls began earning their violent reputations in colonial times when they were trained to participate in a sport called "baiting" in which the dogs were placed into pens with other dogs and animals and forced to fight them.