From Douglas H. Johnson, “Mamdani’s ‘Settlers’, ‘Natives’, and the War on Terror”, African Affairs 108, 433 (2009):

Mamdani extends his South African paradigm, first proposed in his award-winning Citizen and Subject and further elaborated in When Victims Become Killers, to Sudan, whereby the colonial power is said to have imposed a divide between ‘settlers’ and ‘natives’ on the indigenous people, and identified the people of Sudan ‘as members of different races, termed “Arab” and “Zurga” (“black”) earlier and “Arab” and “African” more recently’. This rather assumes that the peoples of Sudan are a tabula rasa on which external powers can inscribe their own vision. The reality of the colonial encounter in the Nile valley suggests otherwise, that the colonial power adopted indigenous categories and terms to describe the peoples it governed.

The Nile valley has a long history of indigenous state building, going back to pharaonic times, and those states have left a legacy not only of social stratification, but of perceptions of race, ethnicity, and social status, and idioms for expressing them. […] Certainly in the northern Nile valley the terms ‘Nubi’ (Nubian), ‘Nubawi’ (Nuba) and ‘Sudani’ (Sudanese) entered colloquial Arabic as synonymous with ‘slave’, and have a very old, pre-nineteenth-century pedigree; while being wholly free was increasingly linked to professing Islam in addition to claiming Arab descent.

These terms were in use when the British occupied Sudan; they were not invented or imposed by the imperial power. They are still in use, with varying degrees of pejorative overtones. If the northern Sudanese intellectuals Mamdani consulted for his introduction to the country have ‘bought into’ these colonial stereotypes, it is because the colonial power ‘bought into’ indigenous classifications. […] Racial categories in Sudan are more a state of mind than of skin colour, and never a clear-cut distinction between black and white (or black and red). While Anglo-American perceptions of race might be misleading when applied to Sudan, perceptions of race and descent still do matter, still do influence how individuals and groups deal with each other, and are still used in the political mobilization of segments of the population. Mamdani’s attempt to dismiss this does not help us understand the continuing complexity of Sudan’s civil conflicts.