Columbia subject headings:
Europe--History--1815-1871.
Europe--History--1871-1918.
Europe--History--20th century.
Harvard subject headings:
Europe--History--1815-1871.
Europe--History--1871-1918.
Europe--History--20th century.
Princeton subject headings:
Europe--History--1815-1871.
Europe--History--1871-1918.
Europe--History--1918-1945.