Columbia subject headings:
Bulgaria--History--1878-1944.
World War, 1914-1918--Bulgaria.
Harvard subject headings:
Bulgaria--History--1878-1944.
World War, 1914-1918--Bulgaria
Princeton subject headings:
Bulgaria--History--1878-1944.
World War, 1914-1918--Bulgaria.
World War, 1914-1918--Diplomatic history.