Columbia subject headings:
Harvard subject headings:
Baltic Sea Region--Commerce--Belgium--History.
Baltic Sea Region--Commerce--Netherlands--History.
Belgium--Commerce--Baltic Sea Region--History.
Netherlands--Commerce--Baltic Sea Region--History.
Princeton subject headings:
Baltic Sea Region--Commerce--Belgium--History.
Baltic Sea Region--Commerce--Netherlands--History.
Belgium--Commerce--Baltic Sea Region--History.
Netherlands--Commerce--Baltic Sea Region--History.