Their enslavers were more than likely fellow brothers in melanin
who sold them to ships to take to America & Europe.
but of course.
It is purely Darwinian in the Jungle. The fittest survive
Those were the lucky ones. The unlucky ones were the slaves who either weren't sold, sold to other Africans or sold to Arabs, who castrated the males and worked both genders to death. Africans took slaves long before the white man started buying them. Heck, Britain and its neighbors bought and sold white slaves right up to around 1000 AD. The Arabs captured white slaves by raiding European coasts up until the 19th century.