Sumner coined ethnocentrism to explain rigid in-group preference

Evidence

Anti-Semitism most commonly appears as a single manifestation of ethnocentrism. The latter term was introduced by William Graham Sumner in his book Folkways (1906). Sumner defined ethnocentrism as a tendency to be rigid in the acceptance of the culturally alike and in the rejection of the culturally unlike. — John T. Jost and Jim Sidanius, Political Psychology, 454

Categorization

• DEFINE: Defines ethnocentrism as Sumner introduced it in Folkways (1906) and positions anti-Semitism as one instance of it.