One of the ironies of the 1960s and 1970s was the sight of African-American activists embracing Islam, entirely ignorant of the fact that Islamic Arabs had enabled the slave trade to thrive for several hundred years. Furthermore, there's also ample evidence of Africans enslaving other Africans and often selling them for profit. Unfortunately, people are often vile to each other, and slavery is one abhorrent manifestation of this tendency.