Due to the war, millions of people met and had children that never would have met had the war not taken place. Millions died that would have had children. It's unlikely any of us would exist had the war not taken place. When it comes to African Americans the likelyhood is that none of them would exist anywhere had it not been for slavery. Their parents never would have met, and even if they had they were not allowed to marry outside their tribe.
Genetics is complicated....
Do the geometric progression, 625,000 soldiers and 1,250,000 civilian deaths. Let;s call it a half million couples who never had kids. Let's see...half million, call it 4 kids each. that's two million. and takes us to, oh, 1885 when those two million start having their 4 kids each, so 8 million Now those 8 million give rise to 32 million, and so on.
So, maybe specific individuals would not have come into being, but the chances that none of us would be around are kind of slim. And like as not there would be more of us all told.
Interesting, though. Are you now saying that slavery was a good thing for Blacks in America?