Anthony Johnson was an indentured servant from Angola. When released at the end of his contract he received the land he was promised and became a free farmer.
Johnson himself hired an indentured servant from Africa. At some point a fire on Johnson’s farm destroyed the contract. The indentured servant wanted to walk away and Johnson wanted him to stay. The case eventually went to court and Johnson won the right to dictate when the contract was up. Johnson simply declared that the contract was never finished and true slavery was born in America.
So Wikipedia said. Most interesting.
Thomas Sowell has observed that research into pre-colonization Africa has suffered because the fact that black-owning-black slavery and slave trading was universal is unacceptable to modern scholarship.