References? The hey day of African chattel slavery followed medieval period, a project of horrific proportions carried out by the society that followed medieva

References? The hey day of African chattel slavery followed medieval period, a project of horrific proportions carried out by the society that followed medieval Europe. As I recall Slavery was legal in medieval Europe but not as widely practiced as serfdom at the time but both were forms of coerced labor (serfs were "slaves of the land" - couldn't leave and had to provide labor or goods). I mean sure, the particular institution of chattel slavery was dying out but this more a matter of "we need something simpler" than any impulse to improvement or any actual improvement.