I’m a bit confused by your reply. Pretty sure the rulers of the Dahomey kingdom weren’t trading with people of the “Americas” but with Europeans, before and after its abolishment across Western Europe. In the book Fistful of Shells, historian Toby Green argues the scale of the trade was only made possible by European traders flooding West Africa with cheap currency (shells which had little value to them but that could be collected in the billions from Brazil and the Indo-Pacific).
My points are:
1. slavery in Western Europe had been abolished long before the transatlantic slave trade - the Europeans were intermediaries, but there was little to no slavery in their home countries. There were many court rulings in England against slavery.
2. not enslaving Christians played a role in abolishing slavery in medieval Europe
3. serfdom was a far better condition that being a slave
4. Slave owners in the Americas opposed the conversion of slaves to Christianity. they also censored the version of the Bible available to slaves very heavily.
5. The claim about mass slavery within Europe is misleading on two counts: serfs are not just chattel slaves (they had rights), and Western Europe was very different from Eastern Europe.
https://www.english-heritage.org.uk/visit/inspire-me/blog/bl...
https://en.wikipedia.org/wiki/Slavery_in_Britain#Judicial_de...
https://en.wikipedia.org/wiki/Select_Parts_of_the_Holy_Bible...