Columbia subject headings:
Bulgaria--Foreign relations--Soviet Union.
Bulgaria--History--Uprising, 1876.
Soviet Union--Foreign relations--Bulgaria.
Harvard subject headings:
Bulgaria--Foreign relations--Russia.
Bulgaria--Foreign relations--Soviet Union.
Bulgaria--History--Uprising, 1876.
Russia--Foreign relations--1855-1881.
Princeton subject headings:
Bulgaria--Foreign relations--Russia.
Bulgaria--History--Uprising, 1876.
Russia--Foreign relations--1855-1881.