The Arab conquest of Egypt (a.d. 641) and of all north Africa (by 711) gave both east and west Africa, Moslem instead of Christian neighbors. The further fact that Moslem shipping speedily took over primacy on the Indian Ocean meant a further exposure of Africa to Moslem infiltration. Until after the year 1000, however, Islam made only modest headway south of the Sahara. There-after, its advance became much more rapid. Ghana, for example, was overthrown in 1076 by a Moslem conqueror. Thereafter Moslem states dominated west Africa. The most important of the early Moslem empires was Mali. The effort required to resist Islamic assault actually generated something of a “golden age” in Abyssinia’s cultural history, but Nubia succumbed to Islam in the fifteenth centnry. After the conquest of Nubia Arab nomad tribes began to move all the way across the African continent, skirting the southern edge of the Sahara. When these migrants reached west Africa they actually rolled back the frontier of cultivation a considerable distance.