Portuguese expansion into the Indian Ocean combined commercial ambition with a religious confrontation between Christianity and Islam. Portuguese strategists sought direct access to eastern goods, especially pepper, and hoped to control the maritime route around Africa. Earlier expeditions also pursued contact with the legendary Christian kingdom of Prester John, believed by the end of the fifteenth century to lie in Africa.

Vasco da Gama’s voyage to India in 1498 marked a decisive turning point. Portugal subsequently became the dominant power on the East African coast and in the Indian Ocean, although East Africa remained secondary to India and the farther Orient. Officials on the coast generally received their orders from the viceroy at Goa, revealing the subordinate position of the region within the Portuguese imperial system.

Portuguese activity relied on bases, treaties, reprisals, and selective intervention rather than a fully organized conquest of the coast. In 1505 a fleet under d’Almeida attacked and sacked Kilwa and Mombasa, and a fort was built at Kilwa as a base, though it was occupied for only seven years. Mozambique and Malindi later became more important bases, while Sofala served the pursuit of gold and ivory.

Portuguese forces also penetrated the Zambezi valley, establishing settlements at Sena and Tete during the first half of the sixteenth century with the permission of the mwene mutapa. Their rivalry with Muslim coastal traders and their attempts to control mines intensified political conflict. The wider consequences included disruption of established commerce, declining coastal city-states, and a costly administration marked by corruption and limited lasting cultural influence.