Until about 1500 South Sudan was mostly controlled by speakers of Central Sudanic languages. Linguistic evidence shows that over time Nilotic speakers, such as the Dinka, Shilluk, and Luo, took over. These groups who currently live around the Sudd marshlands migrated down Southward from Northern and Central Sudan around the time of the collapse of Nubia and the strives that ensued among the many people who were ruled by the Kings of Nubia.

Archaeological evidence shows that a culture based on transhumant cattle raising has been present in that area since 3000 BCE, and the Nilotic culture in that area may thus be continuous to that date. Archaeological evidence as well as the physical evidence in the livlihood of the Nilotes including their dome-shaped houses and tukuls shows that they may have made an enormous contribution to the governance and wealth of the Nubia Kingdom before and during the 25th Dynasty. A few Central Sudanic groups remain such as the Mari and the Moru.

The Nilotic expansion seems to have begun in the 14th century. This coincides with the collapse of the Christian Nubian kingdoms of Makuria and Alodia and the penetration of Arab traders into central Sudan. From the Arabs the South Sudanese may have obtained new breeds of hump-less cattle. 
Archaeologist Roland Oliver notes that the period also shows an Iron Age beginning among the Nilotics. These factors may explain how the Nilotic speakers expanded to dominate the region.

One theory is that it was pressure from the Shilluk that drove the Funj people north, who would establish the Sultanate of Sennar.
The Dinka remained in the Sudd area, maintaining their transhumance economy.

Republic of Sudan
Azande
नीलोटिक विस्तार
First civil war