Slavery is acknowledged and regulated by Islamic law. Islamic rules governing the treatment of slaves are more lenient than those that once prevailed in the Roman and Byzantine empires. Furthermore, Muhammed, a slave owner and slave trader, encouraged his followers to treat their slaves well.
Apologists for Muslim slavery attempt to make the case that Islam is, in fact, opposed to slavery and that the traditional institution of Muslim slavery was humane. However, Muslims like those of other faiths, often ignore those elements of their religion they find inconvenient. There is as a consequence an enormous gulf between the theory and practice of Muslim slavery. Apologists take refuge in theory while critics rely on facts and the facts about Muslim slavery are truly horrible.
A general overview of the Muslim enslavement of black Africans can be found here. It deals not only with the Muslim slave trade in Africa but the European slave trade as well.
Muslim and Arab Turks have always been partial to European slaves and value them more than black slaves. European slaves were acquired through conquest, raids and piracy. As many as a million Christians were enslaved through piracy alone during the 1,200 or so years that Muslims preyed on merchant ships in the Mediterranean Sea and Atlantic Ocean. Muslims in one raid on Iceland took 800 slaves while Muslim pirates ranged as far as Newfoundland. Nearly the entire population of the village of Baltimore in Ireland was enslaved during a Muslim raid in 1631 and other Muslim slave raids were launched against coastal villages in Devon and Cornwall. Many more Christians were enslaved through raids and military conquest. An article about Britains enslaved by Muslim raiders can be found here.
To this enormous number we must add countless Hindus, Sikhs and Buddhists enslaved during the Muslim rape of India. In the end the European and American slave trades are dwarfed by that of the Muslim world.
British and French colonialism ultimately put an end to slavery in much of Africa by seizing and controlling territory and interdicting the trade at sea. America and European powers finally put an end to Muslim piracy in the 19th century. External political, economic and military pressure, largely British, over time forced Muslim nations to ban slavery. Saudi Arabia and Yemen banned it in 1962 while Mauritania has banned it three times, the last one being in 1980. However, the covert practice of slavery continues in Saudi Arabia to this day. Some Saudis living in America have also practiced slavery on American soil.
While Islamic scripture may encourage the good treatment of slaves this guidance has been generally ignored by Muslims. The truth of the matter can be found in the written testimony of those who have been the slaves of Muslims or observed how Muslims treated slaves. There is no shortage of this material. Two reviews of books that touch on the matter can be found here. An excellent article on the subject can be found at The American Thinker.
Winston Churchill in 1899 described what is most deplorable about Islam more concisely than anyone who has written on the subject since.
"How dreadful are the curses which Mohammedanism lays on its votaries! Besides the fanatical frenzy, which is as dangerous in a man as hydrophobia in a dog, there is this fearful fatalistic apathy. The effects are apparent in many countries. Improvident habits, slovenly systems of agriculture, sluggish methods of commerce, and insecurity of property exist wherever the followers of the Prophet rule or live. A degraded sensualism deprives this life of its grace and refinement; the next of its dignity and sanctity.
The fact that in Mohammedan law every woman must belong to some man as his absolute property, either as a child, a wife, or a concubine, must delay the final extinction of slavery until the faith of Islam has ceased to be a great power among men. Individual Moslems may show splendid qualities – but the influence of the religion paralyses the social development of those who follow it. No stronger retrograde force exists in the world. Far from being moribund, Mohammedanism is a militant and proselytizing faith. It has already spread throughout Central Africa, raising fearless warriors at every step; and were it not that Christianity is sheltered in the strong arms of science, the science against which it had vainly struggled, the civilization of modern Europe might fall, as fell the civilization of ancient Rome.”
-Sir Winston Churchill (The River War, first edition, Vol. II, pages248-50 (London: Longmans, Green & Co., 1899).
An article written by a Muslim published in the Bangladeshi newspaper Daily Star provides an enlightened perspective on Muslim slavery past and present. Civilized voices can be found in the Muslim world and this is one of them.
Ask-Imam.com answers the question of whether Muslims can have sex with slave girls today. Today's Muslim slavers and slave owners ignore the Islamic formalities described. Practice in no way resembles theory.