The threat by the leader of Nigeria’s Boko Haram to sell Christian girls into slavery is not an exception to Islamic practice. It is Islamic practice.
Slave raiding by Islamic pirates in the Mediterranean and Atlantic was standard procedure by Turkish and Algerian navies. Those walled towns in Italy, Spain, Portugal, southern France were not defending against Vikings. Some 10, 000 Englishmen were captive in Morocco in the late 1600s.
Corsairs captured thousands of ships, and long stretches of coast in Spain and Italy were almost completely abandoned by their inhabitants, discouraging settlement until the 19th century. From the 16th to 19th century, corsairs captured an estimated 800,000 to 1.25 million people as slaves.[
This compares to the roughly 12 million Africans enslaved in the European slave trade. The figure for Islamic slave raiding is higher but they were at it for longer.
During the 8th and 9th centuries of the Fatimid Caliphate, most of the slaves were Europeans (called Saqaliba) captured along European coasts and during wars. Historians estimate that between 650 and 1900, 10 to 18 million people were enslaved by Arab slave traders and taken from Europe, Asia and Africa across the Red Sea, Indian Ocean, and Sahara desert.
European and American historians assert that between the 8th and 19th century, 10 to 18 million people were bought by Arab slave traders and taken from Africa across the Red Sea, Indian Ocean, and Sahara desert