Columbia subject headings:
Harvard subject headings:
Bulgaria--History--1393-1878.
Bulgaria--Relations--Soviet Union.
Eastern question (Balkan)
Russo-Turkish War, 1877-1878.
Soviet Union--Relations--Bulgaria.
Princeton subject headings:
Bulgaria--History--1393-1878.
Bulgaria--Relations--Russia.
Eastern question (Balkan)
Russia--Relations--Bulgaria.
Russo-Turkish War, 1877-1878.