J26 AFRICAN POLITICAL SYSTEMS
along the eastern side of the western Rift Valley from Lake Albert in the Sudan to Lake Kivu in Ruanda. It is fairly well established that Hamiticized negro peoples migrated southward along this route and that in time this belt of grassland was filled with cattle-keepers. Similarly, climatic conditions made possible the settlement of this area by relatively dense agricultural populations.
But contact due to environmental conditions alone does not account for permanent subjugation, the payment of tribute, and a state structure. Isolation, segregation, and extermination were alternative ways of adjustment. Isolation was not possible, due to the nature of the country and the density of the population. All the Bairu could not move into the relatively small hilly areas. On the other hand, as we have shown, legends relate a stage of segregation before the pressure of Bahima population brought about a general settlement of Ankole by the pastoralists. Extermination was perhaps possible, but the Bahima chose to dominate the Bairu because it paid to dominate. Although the agricultural technique of the Bairu did not produce a great surplus, it could produce, under pressure, enough beer and millet to make domination profitable. In this connexion, wre must always remember that the Bairu had to supply a population only one-tenth its own size. Had the numbers been reversed, exploitation would not, perhaps, have been successful On the other hand, agricultural production was not such that it could have supported the Bahima entirely. The Bahima, then as now, lived upon their cattle and forced their serfs to give them as much beer, millet, and labour as possible without destroying their source of supply. In this connexion, it might be illuminating to contrast the situation in which the Masai found themselves. As they swept down in the extensive plains of the eastern Rift Valley region, they found there only a few wandering Wanderobo hunters who neither interfered with the pastoral habits of the Masai nor offered possibilities for economic exploitation. Exchange relationships were established, but exploitation leading to political domination through a state organization did not arise.
Bahima domination of the Bairu arose not only because these racially and economically different people were brought into contact in large numbers by environmental conditions and because it was economically profitable, but also because the Bahima were able to dominate. Bahima herdsmen, accustomed to protecting