Columbia subject headings:
Christianity and other religions--Islam.
Church history--Middle Ages, 600-1500.
Crusades--First, 1096-1099--History.
Islam--Relations--Christianity--History.
Harvard subject headings:
Crusades--History--Origin.
Crusades.
War--Religious aspects--Christianity--History of doctrines--Middle Ages, 600-1500.
Princeton subject headings:
Crusades.
War--Religious aspects--Christianity--History of doctrines--Middle Ages, 600-1500.