Columbia subject headings:
Harvard subject headings:
Civilization, Medieval--Congresses
Crusades--History--Congresses.
Europe--History--Congresses.
Islamic Empire--History--Congresses.
United States--History--Congresses.
Princeton subject headings:
Civilization, Medieval--Congresses.
Crusades--History--Congresses.
Europe--History--Congresses.
Islamic Empire--History--Congresses.
United States--History--Congresses.