History of Sudan
The modern Republic of Sudan was formed in 1956 and inherited its boundaries from Anglo-Egyptian Sudan, established in 1899. For times predating 1899, usage of the term "Sudan" for the territory of the Republic of Sudan was somewhat anachronistic, and may have referred to the more diffuse concept of the Sudan.
Slavery in Sudan
The "current wave" of slavery in Sudan reportedly began in 1983 with the Second Sudanese Civil War between the North and South. It involved large numbers of "African" Sudanese, "primarily the Dinka, Nuer and Nuba of central Sudan," being captured and sold "(or exploited in other ways)" by Northern Sudanese "Arabs".
The problem of slavery reportedly became worse after the National Islamic Front-backed military government took power in 1989, the Khartoum government declared "jihad" against non-Muslim opposition in the south. The Baggara were also given freedom "to kill these groups, loot their wealth, capture slaves, expel the rest from the territories, and forcefully settle their lands."