"Slaves were the promised booty from Allah and obtaining them was a strong motivation for jihad."
Islam's genocidal attitude toward all non Muslims, and indeed, sometimes within Muslims, is as historical as it has been brutal. Historically, slavery had been another part of the genocidal attitude of "the religion of peace". The genocide in the Darfur region is an instant reminder of the brutal history of Islam and its legacy of slavery - during which time Muslims had also destroyed historical Buddhist structures in Afghanistan in a display of utter disregard for other faiths. Muslims vehemently deny the ugly parts of Islam's history, even those on whose lands it might have occurred, to protect the religion's fabled image of "saviour". In the end, the truth shall set you free - but why are we afraid of the truth even if its initially abrasive?
Islam has bloody past (and possibly present, depending on loyalty) and always will.
Muslims won't acknowledge today's genocidal calls emanating from their religion, even if they're discreetly supportive of their Muslims "brothers'" actions. It would be foolish to expect they would admit past acts of genocide and slavery as per Islam, the flawless religion of all religions, with the mad mob, as it were. Here, an article explains what has been widely known to be true of Islam's slave trade in India and the surrounding region.