Columbia subject headings:
Harvard subject headings:
Europe--Civilization--18th century--Congresses.
Europe--Civilization--19th century--Congresses.
Social classes--Europe--History--Congresses.
Princeton subject headings:
Political science--Europe--History--19th century--Congresses.
Political science--Europe--History--20th century--Congresses.
Social history--19th century--Congresses.
Social history--20th century--Congresses.