I don't think you have any idea about Africa, its history or the people who live there. You also have absolutely no idea what London is or what life there is like.
Africa does not only contain black people. The arabic folk who live in the north are often "white", especially when stood next to someone from the central parts of the continent. Would you exclude these from your idealised state?
As for slavery, you have got that very wrong just like most other people who have not bothered to do proper research. The slave traders who took the slaves from Africa to the Carribean and America Did Not enter the country and capture them in person. The victims were already slaves - captured by other black men - and sold on to the traders. If these slaves did not already exist then the traders would not have bought them; and they would not have gone in looking to capture them themselves because there were too few traders to make viable raiding parties and so they would have been slaughtered.
Therefore the originating source of the black slaves which were used in the cotton fields was actually from other black Africans who raided their neighbours' villages and captured them for sale to the traders.
Also, if you ever take the trouble to get off of your lazy **** and actually visit London then you would see that everybody is free regardless of what colour their skin is. In fact, black people in London (and the rest of the country) are far more free to live their lives than they are in many African countries - and they certainly have safer and better lives than "white" people do in places like Ethiopia.
From your questions, it appears that you have a vivid imagination.
However, you seem to think that London is a country. Before you treat us to another one of your "what ifs", I suggest you take note that London is a city. It's the capital of england and UK.
Take note that Africans enslaved each other long before they saw Europeans.
Lets say you get back to playing with your building bricks and ask mummy to explain to you about some history facts or maybe you are the next big fiction novel writer
what are you -5?
How naive are you? Africans were enslaving other Africans for 100,000 years before they ever saw a white man.
It was African tribesmen who sold African slaves to the whites just so they could get rid of them.
Let say you seem to be about 10 years old
Try asking a question that actually makes some sense and I might be able to answer it.
You need to look at the history books.
What?