The history of slavery in the Muslim world began with institutions inherited from pre-Islamic Arabia. The practices of keeping slaves in the Muslim world nevertheless developed in radically different ways in different Muslim states based on a range of social-political factors, as well as the more immediate economic and logistical considerations of the Arab slave trade. As a general principle, Islam encouraged the manumission of Muslim slaves as a way of expiating sins, and many early converts to Islam, such as Bilal, were former slaves. However, Islam never banned the practice, and it persisted as an important institution in the Muslim world through to the modern era. Throughout Muslim history, slaves served in various social and economic roles, from powerful emirs to harshly treated manual laborers. Slaves were widely employed in irrigation, mining, and animal husbandry, but most commonly as soldiers, guards, domestic workers, and concubines (sex slaves). The use of slaves for hard physical labor early on in Muslim history led to several destructive slave revolts, the most notable being the Zanj Rebellion of 869–883, and led to the end of the practice. Many rulers also used slaves in the military and administration to such an extent that slaves could seize power, as did the Mamluks.Most slaves were imported from outside the Muslim world. Slavery in Islamic law does not have a racial foundation in principle, although this was not always the case in practise. The Arab slave trade was most active in West Asia, North Africa, and Southeast Africa, and rough estimates place the number of Africans enslaved in the twelve centuries prior to the 20th century at between four million to ten million. The Ottoman slave trade came from raids into eastern and central Europe and the Caucasus, while slave traders from the Barbary Coast raided the Mediterranean coasts of Europe and as far afield as the British Isles and Iceland. In the early 20th century, the authorities in Muslim states gradually outlawed and suppressed slavery, largely due to pressure exerted by Western nations such as Britain and France. Slavery in the Ottoman Empire was abolished in 1924 when the new Turkish Constitution disbanded the Imperial Harem and made the last concubines and eunuchs free citizens of the newly proclaimed republic.Slavery in Iran was abolished in 1929. In the Persian Gulf, Saudi Arabia and Yemen abolished it in 1962, while Oman followed in 1970. Mauritania became the last state to abolish slavery, in 1981. In 1990 the Cairo Declaration on Human Rights in Islam declared that "no one has the right to enslave" another human being. As of 2001, however, instances of modern slavery persisted in areas of the Sahel, and several 21st-century terroristic jihadist groups have attempted to use historic slavery in the Muslim world as a pretext for reviving slavery in the 21st century. Scholars point to the various difficulties in studying this amorphous phenomenon which occurs over a large geographic region (between East Africa and the Near East), a lengthy period of history (from the seventh century to the present day), and which only received greater attention after the abolition of the Atlantic slave trade. The terms "Arab slave trade" and "Islamic slave trade" (and other similar terms) are invariably used to refer to this phenomenon. Source: Wikipedia (en)