Columbia subject headings:
Borderlands--Bulgaria--Dimitrovgrad--History--19th century.
Borderlands--Bulgaria--Dimitrovgrad--History--20th century.
Borderlands--Serbia--Pirot--History--19th century.
Borderlands--Serbia--Pirot--History--20th century.
Dimitrovgrad (Bulgaria)--Boundaries--Serbia--Pirot.
Dimitrovgrad (Bulgaria)--History.
Pirot (Serbia)--Boundaries--Bulgaria--Dimitrovgrad.
Pirot (Serbia)--History.
Harvard subject headings:
Borderlands--Bulgaria--Dimitrovgrad--History--19th century.
Borderlands--Bulgaria--Dimitrovgrad--History--20th century.
Borderlands--Serbia--Pirot--History--19th century.
Borderlands--Serbia--Pirot--History--20th century.
Dimitrovgrad (Bulgaria)--Boundaries--Serbia--Pirot.
Dimitrovgrad (Bulgaria)--History.
Pirot (Serbia)--Boundaries--Bulgaria--Dimitrovgrad.
Pirot (Serbia)--History.
Princeton subject headings:
Borderlands--Bulgaria--Dimitrovgrad--History--19th century.
Borderlands--Bulgaria--Dimitrovgrad--History--20th century.
Borderlands--Serbia--Pirot--History--19th century.
Borderlands--Serbia--Pirot--History--20th century.
Dimitrovgrad (Bulgaria)--Boundaries--Serbia--Pirot.
Dimitrovgrad (Bulgaria)--History.
Pirot (Serbia)--Boundaries--Bulgaria--Dimitrovgrad.
Pirot (Serbia)--History.