Columbia subject headings:
Bulgaria--History--1878-1944.
Ferdinand I, Czar of Bulgaria, 1861-1948.
Harvard subject headings:
Bulgaria--History--1878-1944.
Ferdinand I, Czar of Bulgaria, 1861-1948.
Princeton subject headings:
Bulgaria--History--1878-1944.
Ferdinand I, Czar of Bulgaria, 1861-1948.