You're operating on the assumption that they or their ancestors would have all immigrated here at some point. There is absolutely no reason to assume this. African Americans currently constitute about 11% of the population last time I checked... how many are actual immigrants FROM Africa, or mostly descended from WILLING immigrants from Africa? From what I've seen, I doubt that number is even as high as 1 in 100. Therefore it is reasonable to conclude that the vast majority would NOT have immigrated to America from Africa, therefore it is reasonable to assume the vast majority would still be in Africa.... inasumuch as there is ANYTHING resembling reason in this flight of fancy masquerading as a thread.
Fiddling While Rome Burns
Carthago Delenda Est
"I used to roll the dice; see the fear in my enemies' eyes... listen as the crowd would sing, 'now the old king is dead, Long Live the King.'.."
"He who does not think himself worth saving from poverty and ignorance by his own efforts, will hardly be thought worth the efforts of anybody else." -- Frederick Douglass, Self-Made Men (1872)
Africans who live in the few small pockets of Africa where resources are plentiful would be doing just fine.
The overwhelming majority would be living the way most Arabs do today.
Or the way that people in resource-scare areas live all over the world.
Think about places like Western China, Siberia, and interior Australia.
It's hard for anything more than a small, "elite" minority to rise above a stone age existence when an area's resources can't possibly support such an increase in standard of living.
Maybe I missed the post, but I didn't see one single person show either of the two best examples of modern nations that would answer the question in the OP with ease. Take a look at Canada and Great Britain and see how they fare in those two nations.
Our nation has not always lived up to its ideals, yet those ideals have never ceased to guide us. They expose our flaws, and lead us to mend them. We are the beneficiaries of the work of the generations before us and it is each generation's responsibility to continue that work. - Laura Bush