Columbia subject headings:
Denmark--Boundaries--Germany (West)--History--Sources.
Germany (West)--Boundaries--Denmark--History--Sources.
Schleswig-Holstein (Germany)--History--Sources.
Schleswig-Holstein question.
Harvard subject headings:
Princeton subject headings:
Denmark--Boundaries--Germany (West)--History--Sources.
Germany (West)--Boundaries--Denmark--History--Sources.
Schleswig-Holstein (Germany)--History--Sources.