In 1526, the king of Kongo wrote to the king of Portugal and begged him to stop the slave trade. The letters still exist. You can read them. King Afonso I — Nzinga Mbemba. He was not a victim of ignorance about Europe. He was literate in Portuguese, Catholic, and had welcomed Portuguese traders as partners. Then he watched what the trade actually did. He writes that merchants are seizing people every day — nobles, family members, free subjects — and that his country is being emptied. He asks for teachers and doctors instead of ships. He asks, plainly, for it to stop. Portugal's king replied with a letter pointing out how profitable Kongo's trade was and how little else it had to offer. The trade continued for another three hundred years and helped destroy the kingdom. An African head of state put his objection in writing in 1526, in the language of the people doing it, and was told the arithmetic did not work in his favour. "They didn't know" has never been available as an excuse. The correspondence is in the archives.