It's all about bloodline/lineage which goes back hundreds of years. APBTs are bred for their "gameness" which is basically their determination to keep going regardless of injury or threat of injury or pain to themselves. A full grown game dog doesn't socialize with other dogs. Though as pups they'll socialize with their siblings for a bit, but then they have to be separated. Some as early as a few weeks, others take a few months before the aggression towards other dogs kicks in. It's in their blood. You don't have to do anything or force them to fight, it's just something they want to do. Anyone that tells you that you have to force game APBTs to fight[like this nikka below] is an idiot.

Here goes another one. Of course it's brutal, they're trying to tear each other apart, where did I say it was all daisies and roses

And yes sometimes dogs die form their injuries, but it's not a fight to the death. Once a dog quits or refuses to scratch the fight is stopped. Both dogs have to be willing to fight for a fight to continue.
Again, you don't stick a dog in a ring and force it to fight. You'd just lose your money really fast.
Pits>>>>>>>>>>>>>>>>>>>>>>>>>>any other breed
Work ethic, dedication and loyalty is second to none.