There is probably tribalism in everything we see and do to one extent or the other.

Nothing nefarious, necessarily.

You are simply drawn to people that you have things in common with.

Nothing represents this more ridiculously than sports. We literally riot and fight each other over where billionaires choose to locate their sports franchises.

Millionaires, watching multi-millionaires play a game, owned by billionaires. While the middle class and poor watch at home and riot in the street after the championship game.

As distinguished author Isaac Asimov put it in describing our reactions to the contests we view, “All things being equal, you root for your own sex, your own culture, your own locality… and what you want to prove is that you are better than the other person. Whomever you root for represents you; and when he wins, you win.” 

-Robert Cialdini, Influence