Literally none of this is true.
By now, it has become apparent that this man is much dumber than people initially thought, but here is why this specific act of ignorance is so common.
A thread.
Slavery was standard practice throughout Earth until it was almost entirely ended principally by Anglo-American forces in the 19th and 20th centuries. Slavery still exists in some parts of the world btw.
I’m not suggesting Britain was purely angelic, but, nonetheless, this is true.