Religion

Tribe, team, clic, political party, insurrectionist cell,

All are based upon a me and not-me division.
Us and other.

The bricks with which one builds their identity, one's sense of self, put others on the opposite side of a wall.
How defensive one is of their subjective definitions, desires, associations, world-view will reveal how much tribal identity one has.

In the USA, we see a new tribal identity taking place now. Sure tribal identity doesn't have deep roots in American history, if we ignore:

Killing Indians
Massacring non-Mormons
Hanging Africans
Civil War
States
Irish and Italian ghettos in NYC
Republicans