Columbia subject headings:
Balkan Peninsula--Foreign relations--Bulgaria.
Balkan Peninsula--Politics and government.
Bulgaria--Foreign relations--Balkan Peninsula.
Eastern question (Balkan)
Harvard subject headings:
Balkan Peninsula--Foreign relations--Bulgaria.
Balkan Peninsula--Politics and government--19th century.
Balkan Peninsula--Politics and government.
Bulgaria--Foreign relations--Balkan Peninsula.
Eastern question (Balkan)
Princeton subject headings: