Columbia subject headings:
Europe, Northern--Economic conditions--19th century.
Europe, Northern--Economic conditions--20th century.
Harbors--Economic aspects--Europe, Northern.
Port cities--Europe, Northern--History--19th century.
Port cities--Europe, Northern--History--20th century.
Shipping--Europe, Northern--History--19th century.
Shipping--Europe, Northern--History--20th century.
Harvard subject headings:
Harbors--Europe, Northern--History.
Princeton subject headings:
Europe, Northern--Economic conditions--19th century.
Europe, Northern--Economic conditions--20th century.
Harbors--Economic aspects--Europe, Northern.
Port cities--Europe, Northern--History--19th century.
Port cities--Europe, Northern--History--20th century.
Shipping--Europe, Northern--History--19th century.
Shipping--Europe, Northern--History--20th century.