It goes back to Roman times too, throughout the region, and widespread. The Mamluk armies were entirely non-muslim slave armies, mainly of European origin, and persisted for a thousand years until the arrival of Napoleon. Historically it was deeply entwined in the culture.

The first encounter for much of Europe with African slavery were the millions of Europeans who found themselves sold to the African and Arabic slavers or captured by the Barbary pirates. There were even slaving raids to parts of the European coasts in the early Middle Ages.

Which is not to downplay the effects of the trans Atlantic slave trade, just to put it in context a little.