Columbia subject headings:
Harvard subject headings:
Bulgaria--History--Alexander, 1879-1886.
Bulgaria--History--Ferdinand I, 1887-1918.
Bulgaria--History--Interregnum, 1886-1887.
Princeton subject headings:
Bulgaria--History--Alexander, 1879-1886.
Bulgaria--History--Ferdinand I, 1887-1918.
Bulgaria--History--Interregnum, 1886-1887.