The population of Chicago must have something specific in common with the people inhabiting Rwanda, Sierra Leone, and Zimbabwe. Trying to put my finger on it. Must be the food.
You have it. Tribal culture, where those inside the tribe are "people" and those outside the enemy that you can do anything to without moral twinge.
The tribes in the U.S. are the gangs that spring up when the family and Christianity have been taken out of the picture. They are the default position when young men are not taught responsibility, morals, and brought up within a moral framework.