Columbia subject headings:
Harvard subject headings:
Communism--Europe--History--20th century
Popular fronts--Europe--History--20th century.
Socialism--Europe--20th century.
Socialism--Europe--History--20th century
Princeton subject headings:
Communism--Europe--History--20th century.
Popular fronts--Europe--History--20th century.
Socialism--Europe--History--20th century.