Muslims were a silent third party in the formation of modern race.

Evidence

Complicating this history, though, Matar (1999) points to a complex triangle that emerged in the exchange between Christians, indigenous peoples, and Muslims. As the empire of Catholic Spain expanded, it undertook the benevolent role of sending missionaries to spread the work of the Christian God to heathens in the Americas. It was through this interaction that notions of race were consolidated through ideas about nation and religion. — Junaid Rana, Terrifying Muslims, 160