The article deals entirely with aspects of the slave trade in Africa and thus omits another "racially incorrect" fact that makes the same point -- not only were the slaves, but the institution of slavery itself was imported from Africa. Anthony Johnson, the first owner of a chattel slave, not sentenced to servitude as punishment for a crime, (one John Casor) in what was to become the United States, was, like his slave, a black African.
Leftists try to obscure this fact by confusing servitude as a sentence for a crime after a conviction under due process of law, indentured servitude (time limited and by mutual agreement) and actual chattel slavery.