Columbia subject headings:
Harvard subject headings:
Iron industry and trade--Germany--Dortmund Region--History--19th century.
Iron industry and trade--Germany--Dortmund Region--History--20th century.
Steel industry and trade--Germany--Dortmund Region--History--19th century.
Steel industry and trade--Germany--Dortmund Region--History--20th century.
Princeton subject headings:
Iron industry and trade--Germany--Dortmund Region--History--19th century.
Iron industry and trade--Germany--Dortmund Region--History--20th century.
Steel industry and trade--Germany--Dortmund Region--History--19th century.
Steel industry and trade--Germany--Dortmund Region--History--20th century.