People automatically divide the world into in-groups and out-groups.

Evidence

Thanks to the pioneering research of Tajfel and his associates (1978; Tajfel et al., 1971; Tajfel and Turner, 1979), we know that collections of people rather automatically divide the world into in-groups and out-groups. Called the Minimal Group Effect, this tendency has been widely observed in natural groups and even in artificial groups whose members know they have been composed on a purely random basis (Billig and Tajfel, 1973). — Bob Altemeyer, The Authoritarian Specter, 4123

Categorization

• XREF: Connects to the vault’s Christian-nationalism content: the Minimal Group Effect is a candidate mechanism for religious nationalist in-group/out-group dividing.
• QUESTION: Passage cuts off mid-sentence; the full description of the Minimal Group Effect’s reach across natural groups would be worth getting.
• corroborated: 2 independent passages support this claim — Bob Altemeyer, The Authoritarian Specter, 4123