East Africa in 1870 is best defined as the economic hinterland of the commercial entrepôt of Zanzibar. This area included much of what is now Tanzania, Kenya and Uganda, as well as parts of Rwanda, Burundi, Zaïre, Zambia, Malawi, Mozambique and Somalia. The region was criss-crossed by trade routes which converged on the Swahili towns of the east coast. It was along these paths of Swahili expansion that Europeans in the later nineteenth century began to penetrate and occupy the interior. By 1905 Britain and Germany had divided most of East Africa between them, and they had achieved overall command in military and strategic terms. But their new colonial governments exercised a very uneven control over the African population, while the new colonial economies had only partly deflected local labour and capital from older systems of production and exchange. New economic structures were emerging, but their impact was only just becoming evident. Thus the period under study here is very much one of transition. To understand it, we need to consider not only the European innovation but also the local and regional economies, and the wide-ranging Swahili commercial and cultural network. We must also acknowledge the importance of individuals. The changes of the period gave much scope for the exercise of leadership and the pursuit of political rivalry. Initially, African horizons of statecraft were much enlarged, though often one early effect of colonial rule was to narrow them. What follows, then, is a synthesis stressing processes of differential integration in the immediate pre-colonial period, the dynamics of the decade of military conquest, 1888–99, and the terms of reconstruction preparatory to systematic state formation which occurred from the turn of the century until 1905.