Columbia subject headings:
Harvard subject headings:
Bulgaria--Emigration and immigration--History--19th century.
Bulgarians--Soviet Union.
Russia--Emigration and immigration--History--19th century.
Princeton subject headings:
Bessarabia (Moldova and Ukraine)--History.
Black Sea Lowland (Ukraine)--History.
Bulgarians--Bessarabia (Moldova and Ukraine)--History--19th century.
Bulgarians--Ukraine--Black Sea Lowland--History--19th century.