Exactly how? A bankrupt nation has no money to become competitive. The industrial North and all its banks remained just fine. I don't know the economic history of the Civil War but I'll roll the dice and guess it was driven by debt to foreign nations just like the Revolutionary War was.
Blacks remained in the South as agrarian sharecroppers anyways, which for them was essentially slavery (financially) except that their body and person was not owned by another, just their labor. And violence still was used in the South all the way into what... the damned 1960s?
This woman was too young to have even been born in the late 1800s but she still recalls violence used on the sharecropping fields of the South she toiled on.
This man claims it took place, too, and not just by white men but angry black men intent on inflicting pain on black women that worked in the fields with them.
Here is a video of an elderly woman that had a grandfather that lived as a child seeing slavery, his enslaved black mother, on a Southern plantation. He was mulatto and his father was the slave owner of the plantation. His father and his father's white wife treated him good.
But yes... slavery was not the only thing that economically propelled the USA forward. Industrialization did and it grew the US economy exponentially. Countries like the USA and Brazil are helped by their land size (and its diversity) which are the size of "continents." Hell, England is small enough to fit in side the State of California. So, while there is mass poverty throughout Brazil, that does not prevent Brazil from having one of the largest GDPs on earth. It's land produces so much value and there is so much of that land. Like the United States.
The United Kingdom is a series of countries (like the EU is) and not a single country like England is. England presides as the head of the United Kingdom. Germany and Brazil and the USA are single countries though.
https://en.wikipedia.org/wiki/List_of_countries_by_GDP_(nominal)