Islam served as Europe’s principal civilizational other for centuries.

Evidence

For centuries, Europe’s main other has been the world of Islam. Defining episodes in European history - Muslim domination of the Mediterranean during the early Middle Ages, the conquest of Spain, the Crusades, the fall of Constantinople, the siege of Vienna refer to Islam. — David Theo Goldberg, John Solomos, A Companion to Racial and Ethnic Studies, 193