Columbia subject headings:
Ruhr (Germany : Region)--Economic conditions.
Ruhr (Germany : Region)--History.
Ruhr (Germany : Region)--Intellectual life.
Ruhr (Germany : Region)--Politics and government.
Harvard subject headings:
Industries--Germany--Ruhr (Region)--History.
Ruhr (Germany : Region)--Economic conditions
Princeton subject headings:
Ruhr (Germany : Region)--Economic conditions.
Ruhr (Germany : Region)--History.
Ruhr (Germany : Region)--Intellectual life.
Ruhr (Germany : Region)--Politics and government.