Columbia subject headings:
Strikes and lockouts--Germany--Ruhr (Region)--History--19th century.
Working class--Germany--Ruhr (Region)--History--19th century.
Harvard subject headings:
Strikes and lockouts--Germany--Ruhr (Region)--History--19th century.
Working class--Germany--Ruhr (Region)--History--19th century.
Princeton subject headings:
Strikes and lockouts--Germany (West)--Ruhr (Region)--History--19th century.
Working class--Germany (West)--Ruhr (Region)--History--19th century.