The American Bulldog is a large breed of utility dog descended from the now-extinct Old English Bulldog. At some point, Scott began infusing non-Johnson catch bulldogs from working Southern farms with Johnson's lines, creating what is now known as the Standard type American Bulldog, also called the Scott type. At another point, Johnson began crossing his original lines with an atavistic English bulldog from the North that had maintained its genetic athletic vigor, creating the Bully type American Bulldog, also known as the Johnson type or the Classic type. This is a large breed that must not become a frog in a well that only knows its home territory and it must be trained out of the dog immediately if the dog is obtained past the age of 18 months. American Bulldogs are a known breed that will destroy furniture and shoes if they are not given enough to do and this is yet another reason too much isolation is disastrous for this breed.Fear- or aggression-causing triggers can include other dogs, children it does not know, postal workers, and strangers.