Columbia subject headings:
Harvard subject headings:
Labor movement--Germany--Ruhr (Region)--History--20th century.
Miners--Labor unions--Germany--Ruhr (Region)--Social conditions--20th century.
Socialization--Germany--Ruhr (Region)--History--20th century.
Strikes and lockouts--Miners--Germany--Ruhr (Region)--History--20th century.
Princeton subject headings:
Labor movement--Germany--Ruhr (Region)--History--20th century.
Miners--Labor unions--Germany--Ruhr (Region)--Social conditions--20th century.
Socialization--Germany--Ruhr (Region)--History--20th century.
Strikes and lockouts--Miners--Germany--Ruhr (Region)--History--20th century.