Columbia subject headings:
Labor movement--Germany--Hamburg--History--Congresses.
Labor movement--Germany--History--Congresses.
Harvard subject headings:
Labor movement--Germany--Hamburg--History--Congresses.
Labor movement--Germany--History--Congresses.
Princeton subject headings:
Industries--Germany--History.
Labor movement--Germany--Hamburg--History.
Labor movement--Germany--History.
Labor unions--Germany--History.