Southern Dobruja, South Dobruja, or Quadrilateral (Bulgarian: Южна Добруджа, romanized: Yuzhna Dobrudzha or simply Добруджа, Dobrudzha; Romanian: Dobrogea de Sud, Cadrilater or Dobrogea Nouă) is an area of north-eastern Bulgaria comprising Dobrich and Silistra provinces, part of the historical region of Dobruja. It has an area of 7,412 square km[1] and a population of 358,000.
It is historically noteworthy as a point of contention in Bulgarian-Romanian relations. Part of Bulgaria between 1878 and 1913, the region was annexed by Romania in the Treaty of Bucharest (1913), targeted by Bulgaria during World War I (1914–18), and subsequently remained Romanian until 1940, when Bulgaria regained control in the Treaty of Craiova, which went along with a compulsory population exchange. Southern Dobruja has been part of Bulgaria since 1940.