Explanation, or the identification and assessment of the causes of events and situations, occupies the central place in nearly all historical writing in the present century. It is also the aspect of history which is most keenly debated by philosophers, and is the main issue today in the unending, wearisome, but seemingly inescapable controversy as to whether history belongs, or belongs more, with the sciences or with the humanities. The scientific or positivist school, numbering among its recent exponents Popper and Gardiner, emphasizes the extent to which historical explanation attains a regularity akin to, though not identical with, that found in the physical and other sciences, Hempel adding the contention that such explanation can always, and often should, be reduced to a ‘covering law’, or single universal statement subsuming the whole explanation. The idealists, among whom Croce, Collingwood, and most recently Oakeshott are prominent, stress conversely the uniqueness of history, and Dray has reinforced their position by his attack on the covering law thesis. The debate is one in which historians themselves have taken little part, and African historians none at all, despite its crucial importance for almost every aspect of their profession. Yet it is a debate which needs continuous illustration from the historiographical process, a need which historians are best able to meet. The aim of the present article is to contribute to the debate by examining as a problem in historical explanation the fall of Oyo, the powerful state of the northern Yoruba, in the early nineteenth century.