Columbia subject headings:
Harvard subject headings:
Catholic Church--Foreign relations--Congresses.
International relations--Congresses
Papacy--History--19th century--Congresses.
Papacy--History--20th century--Congresses.
Princeton subject headings:
Catholic Church--Foreign relations--Congresses.
International relations--Congresses.
Papacy--History--19th century--Congresses.
Papacy--History--20th century--Congresses.