Columbia subject headings:
Germany--History--20th century--Congresses.
Germany--History--Unification, 1990--Congresses.
Harvard subject headings:
Germany--History--20th century--Congresses.
Germany--History--Unification, 1990--Congresses.
Princeton subject headings:
Germany--History--20th century--Congresses.
Germany--History--Unification, 1990--Congresses.