The American Bulldog as we know it today is a breed with considerable genetic diversity. Their ancestry can be traced back to England in the 1600s, when the word "bulldog" was used to describe the work performed by a dog rather than any particular look. As the occasion for bulldog work dwindled during the industrial revolution and the "sport" of bull baiting became illegal, bulldogs fell out of favor and were regarded as a dog of the lower social classes. Some breeders and historians believe that it was English immigrants colonizing America that were largely responsible for preserving this breed as a working dog. These immigrants brought many of their prized working bulldogs to the colonies. In this new land they would need dogs with sufficient size, intelligence and endurance to undertake a variety of tasks, a true utility dog.

How much of the original (bull baiting type) bulldog that exists in today's American Bulldogs is anybody's guess. Interbreeding with the Catahoula, APBT, English bulldog, Olde English Bulldogge, Boxer, Mastiff, St. Bernard or others makes "purity" difficult to define. Some lines are obviously closer to the original type than others, even allowing for the wide variation in type caused by such a diverse gene pool. Thus the American Bulldog of today was created by chance as much as by design. There was no Herr Louis Doberman (creator of the Doberman Pinscher) or David Leavitt (creator of the Olde Bulldogge) to document the creation of this breed from scratch. Rather, it has evolved from a number of indigenous American working breeds combined with the blood of the descendants of those original English Bulldogs. Working ability and general aptitude in the performance of a variety of tasks were the main criteria for breeding and selection.

It has not been until relatively recent times that the actual look of the dog was considered to be of much importance. Many breeders have fallen into the trap of placing too much importance on attributes such as head size and shape, weight, type of bite, color, etc, without considering the effects of these on performance. The American Bulldog is still being used today in the capacity for which it was originally bred, that is, family companion and guardian, hunting wild game, predator control and catching free range cattle. They have the heart and strength to perform almost any task well. Because the American Bulldog is a breed with considerable genetic diversity, it does not fit snugly into the "cookie cutter" mould of the traditional Show world. This is a fact that some find hard to accept, particularly since it means that there is a great deal of dissimilarity between dogs of supposedly the same breed.

The principal architects of today's American Bulldog are Allen Scott and John D. Johnson. In 1970, John D. Johnson and Alan Scott first registered the American Pit Bulldog with the NKC, and later renamed it to the American Bulldog to avoid confusion with the American Pit Bull Terrier. Prior to that the dogs were known by a variety of different regional names: Southern White, Hill Bulldog, Country Bulldog, White Bulldog, White English Bulldog, English White, and commonly just "Bulldog". 

As well as having varying names according to region, they also had local bloodline variations in appearance and size and also differences according to the tasks intended of them by their breeders and this is part of the reason why the American Bulldog breed conformation standards laid down by the registries allow for such a wide variation in type. 

Initially Scott and Johnson had similar dogs and they freely bred and traded dogs with each other. Johnson's Dick the Bruiser and Scott's Mac the Masher were their foundation dogs. These two dogs were Old Southern Whites. Alan Scott and John D Johnson scoured the mountains and valleys of those Southern states looking for bulldogs and buying up those that they liked and they began a breeding program together. 

Later on they had a falling out and JDJ began to develop and refine his trademark heavier-built style of American Bulldog. From the breeding programs of these two men, two distinct strains have emerged, commonly called the Johnson type or the Bully/Classic class and the Scott type or Standard/Performance class. The main registries have subdivided the breed standard into these two distinct phenotypes, but these distinct types having diverged and having been diluted it is now more appropriate to talk about 5 types:

1. The Bully / Classic / JOHNSON Type:
The Johnson type resembles an athletic, tightly built, white Bullmastiff. As compared to the Scott type it is a larger, wider dog with more bone, pendulous lips, and undershot jaw, facial wrinkles and a shorter muzzle. In the 70s John D. Johnson bred two of his American Bulldog females (King's Lady Grace and Johnson's Sugar Doll) to English Bulldog West Champ's High Hopes. This created Johnson's Sugar Doll 3 and Bullmead's Queen who were both half English Bulldog. The famous Johnson American Bulldog Johnson's Incredible Mean Machine was 30% English Bulldog and foundation stock for most Johnson American Bulldogs today. This has made the Johnson type American Bulldog somewhat less athletic and more bully in appearance. Weight for males can be 55 kg plus. Mr. Johnson has branched away from the American Bulldog in 1998 to create the JDJ bulldog, which is a very tall dog with a "Standard type" body and a "Bully" head. Some claim this is now to be considered a different breed, registered with John D. Johnson.

2. The Standard / Performance/ SCOTT Type:
The Scott type looks like a large, coarse, leggy, white Pit Bull. They are lighter weight than the Johnson type and have a very muscular athelic look and their front legs are under their body, not thrown out to the sides. This makes the standard type American Bulldog very agile and structurally sound. They have a very strong prey drive and can be dog aggressive, which is exactly what American Bulldogs needed 300 years ago to protect the farm from wolves and coyotes, and to do catch work. The Scott type has a closer underbite and longer muzzle too. Weight generally from 27 to 45 kg. Well-known lines include Scott, Hines, Kerschner, Koura, Stover, and Williamson among others.

3. The Painter/Margentina Type:
In the late 1970s, Joe Painter, Margentina, Tappe and others developed a second performance strain of American Bulldogs that was unfortunately used in the dog fighting arena. They are of an even smaller size, 25 to 35 kg. This American Bulldog line came from using inbred Johnson's Dick the Bruiser females that were small between 20 to 30 kg. They were bred to Larry Wrights Rounder and Alan Scott's Big Bucks. The Rounder dog came from G.L. Williamson's Big Joe and Tuck's Tiger Lady who was 50% Mac the Masher. It is widely rumored that Margentina and Trap infused Pit Bull Terrier blood into the pure Joe Painter line. This was probably due to the color in these dogs. However some of the dogs Joe Painter already had that color in them. A couple of their more famous dogs were Painter's Zeke and Margentina's Sargent Rock.The Painter/Margentina strain was heavily inbred and had some problems, though through judicious outcrosses, the Painter strain has made valuable contributions to the breed as a whole.

4. The "Old Southern Whites" Type:
One can still find dogs referred to as "White English" among countrymen that never have heard about Mr. Scott or Mr. Johnson. This is a term for the original country bulldogs that are not descended from any of the modern lines, i.e. breeds strains with no infusion of blood from the common American Bulldog lines. The reverse is in fact the truth; that is to say Old Southern Whites were the raw material that Scott, JDJ and others started out with when they got their foundation dogs. Southern Whites are still used by country folk in the deep south, some of whom have probably never heard of Mr Scott or Mr Johnson or the term "American Bulldog". Often their families have bred these "White English" for generations and these are the dogs that some claim should be named "The true American Bulldogs". A few breeders still use pure Southern White lines in their breeding programs and they can be a useful source of fresh genetic material for established bloodlines.

5. The "Hybrid" Type:
These are basically American Bulldogs whose blood-lines are a mixture of standard and bully types, with the goal being to distill the best features of both. Today most American bulldogs are probably in this category. Some notable successful breeders of hybrid lines include Kyle Symmes (Sure-Grip), Matt Boyd and Greg Souza among many others. Hybrid dogs have excelled in competition in the States, especially Schutzhund and similar disciplines.

There are arguments today over which strains are superior (or inferior!) and which are closer to the original bulldogs of old England. It is my belief that whilst people are entitled to like whatever dogs they want; it is the performance type of American Bulldog that more closely resembles the bulldogs of old both in form and function.

The performance type of American Bulldog enjoys superior longevity and better overall health than its non-performance counterpart. This is, of course, not to say they are devoid of health problems, but they certainly have fewer. The non-performance type of American Bulldog tends to show more characteristics of the Mastiff, English Bulldog, Bullmastiff, Dogue De Bordeaux and Saint Bernard. This is due to the infusions made by some breeders in an effort to increase size and weight. Many of the dogs from these lines suffer from genetic defects ranging from thyroid disorders to undersized heart and lungs; reduced tolerance to heat and cold and a shorter lifespan.