Columbia subject headings:
Bulgaria--History--1393-1762--Sources.
Nikopol Region (Bulgaria)--History--Sources.
Turkey--History--1453-1683--Sources.
Harvard subject headings:
Bulgaria--History--1393-1762--Sources.
Nikopol Region (Bulgaria)--History--Sources.
Turkey--History--1453-1683--Sources.
Princeton subject headings:
Bulgaria--History--1393-1762--Sources.
Nikopol Region (Bulgaria)--History--Sources.
Turkey--History--1453-1683--Sources.