Religion most often defines civilizations and can override shared ethnicity and language.

Evidence

Blood, language, religion, way of life, were what the Greeks had in common and what distinguished them from the Persians and other non-Greeks. Of all the objective elements which define civilizations, however, the most important usually is religion, as the Athenians emphasized. To a very large degree, the major civilizations in human history have been closely identified with the world’s great religions; and people who share ethnicity and language but differ in religion may slaughter each other, as happened in Lebanon, the former Yugoslavia, and the Subcontinent. — Samuel P. Huntington, The Clash of Civilizations and the…, 110 (#expands, via linked claim)

Categorization

• XREF: connects to: Language loyalty overrides religious division to unify Sinhalese against Tamils. — Neil DeVotta, Sinhalese Buddhist Nationalist…, 241; The Persian term for nation originally designated a religious community. — Nadim N. Rouhana and Nadera Shalhoub-Kevorkian, When Politics Are Sacralized:…, 1666; Religion is the most important element defining civilizations — Samuel P. Huntington, The Clash of Civilizations and the…, 110 (+6 more)

Broader Connections

• Religion is the most important element defining civilizations #expands (0.95) — Samuel P. Huntington, The Clash of Civilizations and the…, 110