Columbia subject headings:
Harvard subject headings:
Denmark--Relations--Germany--Schleswig-Holstein--Congresses.
Schleswig-Holstein (Germany)--History--Congresses.
Schleswig-Holstein (Germany)--Relations--Denmark--Congresses.
Princeton subject headings:
Denmark--Relations--Germany--Schleswig-Holstein--Congresses.
Schleswig-Holstein (Germany)--History--Congresses.
Schleswig-Holstein (Germany)--Relations--Denmark--Congresses.