The British Royalty as well as Portuguese, Dutch, and French firms were all in the slave trading business. Packed human beings like sardines down in the bilge. If we are gonna do this we need to send them a bill. That cheap slave cotton went straight to UK textile mills. It is no secret why the confederate battle flag looks a lot like the union jack. Eventually the overseas slave trade fell off because states like Virginia were essentially raising slaves and selling them to farmers in the new slave states.
https://en.wikipedia.org/wiki/Royal_African_Company
As an aside, imagine if the government requires DNA to establish claims. Not sure I would love that.