The arrival of colonialism
Portuguese traders dominated the East African coast from 1525 until the early 18th century, when Omani Arabs once again regained control of the slave trade. The first missionaries journeyed to the mainland in the early 19th century and settlements, mission stations, and trading posts were built as far inland as Lake Tanganyika.
In the late 19th century, the German East African Company gained control of large portions of the Tanzanian mainland, although the British held a sphere of influence over the Omani sultans ruling the Zanzibar Archipelago. By 1891, most of mainland Tanzania was under the colonial administration of German East Africa.