I strongly, strongly suggest you revisit some of the preconceptions that led you here. I was going to instinctually retort, but instead took 5 minutes to read the relevant Wikipedia article on the topic: https://en.m.wikipedia.org/wiki/Slavery_in_Africa#West_Africa. It is clear that the topic is more nuanced than I originally thought, so thank you for bringing that to my attention, but it’s a crude and broad brush to imply that most slaves already existed in slavery prior to the Atlantic trade. There is also a significant difference between slaves in Africa who were exchanged between local groups in a wholly African context, versus slaves chained up and flung across the Atlantic with a 12% mortality rate and forced under a European slavery conception.
I suspect your response has rubbed others the wrong way, as it did myself, so consider this an attempt to find a common ground for dialogue - whatever the history of Africs prior to the Atlantic Slave Trade, I think we can agree that what happened was utterly grotesque and an atrocity upon the history of our common humanity.
I strongly suggest for anybody who has a problem with what I said to actually just read the Wikipedia article about the Atlantic slave trade. Litterally the second sentence of the article is:
The vast majority of those who were transported in the transatlantic slave trade were people from Central and West Africa who had been sold by West African slave traders to mainly Portuguese, British, Spanish, Dutch, and French slave traders.
Obviously this is a dark chapter in human history, which makes it even more necessary to say the truth about it, as to not repeat it. Also really important is to read the part about what Africans did know about the slave trade, which was more then you seem to believe..
I hope you read it, as only the truth can help prevent something like this to happen again.