Columbia subject headings:
Harvard subject headings:
Essen (Germany)--History--20th century.
Germany--History--Revolution, 1918
Labor unions--Germany--Essen--History--20th century.
Strikes and lockouts--Germany--Essen--History--20th century.
Princeton subject headings:
Social movements--Germany--Essen--History--20th century.
Socialism--Germany--Essen--History--20th century.
Working class--Political activity--Germany--Essen.