This page rates breeds in dog combativeness. It gives the breeds a rating
that is typical of the breed, however, this is not written in stone. If dogs are
raised together and well socialized, they can be good friends. Notice the Jack
Russell Terrier and the American Pit Bull Terrier in the photos below. They are
an example of two breeds who are typically very dog aggressive. But they get
along great with their fellow canine family members.