Factionalism
A group of people in a bigger group who all stick together, even if it means fighting everyone else. They're like the cool kids in the class, but worse.
My group is a faction because we all think we're the best and the others are losers.
My best friend and I are a faction because we don't like the other kids in the class.
My cousins are a faction because they think they're the most important people in the world.