Columbia subject headings:
Coal miners--Germany--Ruhr (Region)--History.
Coal miners--Labor unions--Political activity--Germany--Ruhr (Region)--History.
Ruhr (Germany : Region)--Social conditions.
Harvard subject headings:
Coal miners--Germany--Ruhr (Region)--History.
Coal miners--Labor unions--Germany--Ruhr (Region)--Political activity--History.
Coal miners--Labor unions--Political activity--Germany--Ruhr (Region)--History.
Ruhr (Germany : Region)--Social conditions
Princeton subject headings:
Coal miners--Germany (West)--Ruhr (Region)--History.
Coal miners--Labor unions--Germany (West)--Ruhr (Region)--Political activity--History.
Ruhr (Germany : Region)--Social conditions.