Columbia subject headings:
Danube River.
International rivers.
Harvard subject headings:
Danube River Region--History.
Danube River Region--Strategic aspects--History--19th century.
Danube River--Commerce--History--19th century.
Princeton subject headings:
Danube River Region--History.
Danube River Region--Strategic aspects--History--19th century.
Danube River--Commerce--History--19th century.