Columbia subject headings:
Harvard subject headings:
Communism--Germany--History--20th century
Germany--Politics and government--1888-1918
Germany--Politics and government--1918-1933
Socialist parties--Germany--History--20th century.
Sozialdemokratische Partei Deutschlands--History.
Princeton subject headings:
Center parties.
Deutsche Zentrumspartei--History.
Right and left (Political science)
Sozialdemokratische Partei Deutschlands--History.