The East African coast was a part of the commercial system in the Indian Ocean for at least two thousand years. But its role in that system for most of that period was largely that of an intermediate zone of exchange between various producing and consuming zones around the ocean. Commerce, rather than production, formed the basis of the civilisation that flourished there. It was cosmopolitan and urbane; it was prosperous but compradorial. The coast was a zone of interaction between two cultural streams, one coming from the African interior and one from across the Indian Ocean, from which emerged a synthesis, the Swahili civilisation, that at every step betrays its dual parentage. But that civilisation was mercantile. It gave rise to city-states that were like beads in a rosary, each forming a distinct entity, and yet threaded together by maritime communication and a common culture and language. Their mercantile ruling classes prospered from the middleman's profit which they cornered. They were utterly dependent on international trade, with no control over either the producing or consuming ends. The rhythm of Swahili coastal history was not internally generated but was synchronised with the wider rhythm of international trade in the Indian Ocean, and of some of the dominant social formations in that system.

The East African coast forms a fairly distinct geographical entity, bounded on the west by a belt of poor, low-rainfall scrub known in Kiswahili as the nyika(wilderness). The nyikaruns just behind the narrow coastal belt in Kenya. Further south, it is more broken, being penetrated by the eastern rim of mountains and by river valleys which form corridors into the interior. The nyikarecedes further into the interior, virtually disappearing in southern mainland Tanzania. The character of the narrow coastal belt, especially in the north, meant that it failed to provide an adequate productive base for many of the city-states, some of which were confined to offshore islands. Moving from north to south, however, there is a progressive enlargement of the immediate hinterland, and the potential for production and trade. On the other hand, the nyikaimposed not so much an absolute barrier as a premium on the costs of communication between the coast and the interior, a price that could be paid only at certain times and places in the history of East Africa.