Islam created a new situation by prohibiting the enslavement not only of freeborn Muslims but even of freeborn non-Muslims living under the protection of the Muslim state. The children of slaves were born slaves, but, for a number of reasons, this source of recruitment was not adequate. The growing need for slaves had to be met, therefore, by importation from beyond the Islamic frontier. This gave rise to a vast expansion of slave raiding and slave trading in the Eurasian steppe to the north and in tropical Africa to the south of the Islamic lands. It is for this reason, no doubt, that the massive development of the slave trade in black Africa and the large scale importation of black Africans for use in the Mediterranean and Middle Eastern countries date from the Arab period.
In one of the sad paradoxes of history, this resulted from one of the most important of the liberalizing and humanizing changes that the Islamic dispensation brought to the ancient world.
The Crows of the Arabs, Bernard Lewis
Source: Critical Inquiry, Vol. 12, No. 1, "Race," Writing, and Difference (Autumn, 1985), pp. 88-97