Cordoba Fighting Dog
The Cordoba Fighting Dog originated in Argentina and was a cross between a Mastiff, Bull Terrier, and Old English Bulldog. It is now extinct, but it was used in the creation of the Dogo Argentino, so its ancestry lives on.
Many of the dogs in the breed died fighting. Some were used in dog fighting pits, and some were so aggressive that they fought the opposite gender rather than mating. Both of these problems led to the extinction of the breed.