Both ideas serve as powerful justifications for holding an entire race in bondage. Thanks Thought Bubble, but there were even more contributors to the ideas that led to Atlantic slavery. For instance, Muslim Arabs were the first to import large number of Bantu-speaking Africans into their territory as slaves. The Muslims called these Africans Zanj, and they were a distinct and despised group, distinguished from other North Africans by the color of their skin. The Zanjan territory held by the Abbasids staged one of the first big slave revolts in 869 CE, and it may be that this revolt was so devastating that it convinced the Abbasids that large-scale plantation-style agriculture on the Roman model just wasn't worth it. But by then they'd connected the Aristotelian idea that some people are just naturally slaves with the appearance of sub-Saharan Africans. The Spanish and the Portuguese, you no doubt remember, were the Europeans with the closest ties to the Muslim world because there were Muslims living on the Iberian Peninsula until 1492, so it makes sense that the Iberians would be the first to absorb these racist attitude toward blacks.