The expansion of the Sokoto Caliphate into the lands of the diverse non-Muslim peoples of the Middle Belt area is a familiar theme in the nineteenth-century history of the Central Sudan. As the Middle Belt is known to have an overall lower population density than adjoining areas to the north and south, the explanation has been proposed that this was due to slave raiding by Muslim states. A study of the history of this area does not support this overall view, even though it might be accepted with reference to limited areas. areas. It can be shown, moreover that in certain localities populations were actually enhanced as a result of the consolidation of Muslim power, while others, currently of extremely low density, were completely unaffected. If the factors affecting population in this area are to be understood, reference to over-simplified causes such as slave raiding must be shunned. Geographical and biological factors influencing population growth may be more fertile areas of enquiry.