Slavery was practiced since ancient times in Africa. In East Africa slavery was introduced during trade contacts with the Middle East and Far East as early as 2 AD. However slavery was only practiced on a small scale.
Slaves were used as farm laborers, domestic servants, guards or soldiers but they were also entitled to some rights. The reasons for the expansion of slave trade in East Africa during the 18th century includes:-
1. Great demands for slaves as soldiers and domestic servants in the Muslim nations of Arabia. Thus the slaves had to come from non Muslim regions like the interior of East Africa. There were major slave markets in Zanzibar, Bagamoyo, Pemba, Kilwa,Mikindani and Mombasa.
2. Slaves were needed as porters, they ferried goods such as ivory and gold from theinterior of Africa to the coast, especially to the American, Indian and British traders whotook part in it.
3. Portuguese slave traders supplied slaves to the Portuguese coffee and sugar plantations in Brazil. In the first half of 18th century Portuguese expanded their plantations. So their source of slaves in West Africa and Mozambique became inadequate hence they came in East Africa.
4. High demand for slave labour in French sugar plantations in Mauritius and Reunion Island. Initially the French depended slaves fro Mozambique but by the 1770s the demand exceeded supply as a result the French came further North to East Africa in search of slaves.