Short answers, pulled from the story.
Southern Dobruja is a region of north-eastern Bulgaria covering 7,412 square kilometers, comprising the Dobrich and Silistra provinces. It is part of the historical region of Dobruja and has a population of around 358,000.
Southern Dobruja was ceded to Romania under the Treaty of Bucharest in 1913, following Bulgaria's defeat in the Second Balkan War. It had been part of Bulgarian territory since 1878.
On the 7th of September 1940, Southern Dobruja was restored to Bulgaria under the Treaty of Craiova. The treaty required a compulsory population exchange in which about 110,000 Romanians, Aromanians, and Megleno-Romanians left Southern Dobruja, while roughly 77,000 Bulgarians left Northern Dobruja.
In 1910, Southern Dobruja had 282,007 inhabitants. Bulgarians made up 47.6 percent, Turks 37.8 percent, Roma 4.3 percent, Tatars 4.2 percent, and Romanians about 2.3 percent.
In 1914, Romania required landowners in Southern Dobruja to surrender one third of their claimed land or pay its cash equivalent. Much of the redistributed land went to settlers including tens of thousands of Aromanians from Macedonia and Romanians from Wallachia, leading to claims the policy had a nationalist purpose.
By the 2001 census, only 591 Romanians remained in Southern Dobruja, rising slightly to 947 by 2011. Almost 95 percent of the Romanians who had lived there before 1940 had settled in the region only after 1913 and were displaced by the Treaty of Craiova population exchange.