Slaves in Africa could work earn their freedom. Slaves there were either war captives, criminals, or there were some used for sex. At least 1 former slave became a king, Jaja of Obobo.
en.wikipedia.org
And it was more than just about class. I'm reading "Stamped from the Beginning" and it goes into great detail about the various theories that justified racism and enslavement. But the biggest problem with the Africans selling other Africans problem in America is ths:
“In fact, most American slaves were not kidnapped on another continent. Though over 12.7 million Africans were forced onto ships to the Western hemisphere, estimates only have 400,000-500,000 landing in present-day America. How then to account for the four million black slaves who were tilling fields in 1860? “The South,” the Sublettes write, “did not only produce tobacco, rice, sugar, and cotton as commodities for sale; it produced people.” Slavers called slave-breeding “natural increase,” but there was nothing natural about producing slaves; it took scientific management. Thomas Jefferson bragged to George Washington that the birth of black children was increasing Virginia’s capital stock by four percent annually.”
Ned & Constance Sublette,
The American Slave Coast: A History of the Slave-Breeding Industry, Chicago, Lawrence Hill Books, 2016
“According to database-backed estimates by David Eltis and David Richardson, only about 389,000 kidnapped Africans were disembarked in the ports of the present-day United States, the majority of them before independence.” “By 1860, those few hundred thousand Africans had given way to four million African Americans.”
Ned & Constance Sublette,
The American Slave Coast: A History of the Slave -Breeding Industry
According to this information , 389,000 slaves landed on the shores of what is now America. By 1860, there were four million slaves living here. The importation of slaves was made illegal in 1808. So from 1808 until 1860, the number of slaves increased by at least one thousand percent. If we allow for the Africans selling each other, Africans would be responsible for approximately 389 thousand slaves. What about the 3.1-4 million additional slaves? Africans did not create them.
The white controlled slave breeding "industry" IN AMERICA created 10 times more blacks than the number that came from Africans who "sold other Africans".