Columbia subject headings:
Harvard subject headings:
Crusades--13th-15th centuries--Congresses.
Eastern question--Congresses.
Europe--History--1492-1648--Congresses.
Geopolitics--Europe--Congresses.
Princeton subject headings:
Christianity and politics--Europe--History--Congresses.
Crusades--13th-15th centuries--Congresses.
Europe--Foreign relations--Middle East--Congresses.
Middle East--Foreign relations--Europe--Congresses.