The irony is that slavery was a dying institution before the Civil War. Even in the South.
Importation of new slaves was already banned.
More states were banning on it own their own.
Abolition movements, founded in churches, were making political gains in the South.
But the largest reason was that slavery was no longer economically feasible. The industrial age was dawning. Factories, mass production, automation, etc.
It made no economic sense to feed, house, cloth and provide medical care for an investment that did not cash flow.
And PS - I am sure HBO will IGNORE:
The first slave owner in America was a free black.
There were plenty of free blacks who owned slaves.
There were plenty of white slaves.
An accurate alternate timeline would actually be:
Lincoln doesn’t die
Reconstruction actually works
Blacks become socially and economically integrated
Segregation ends many decades before it actually did
Of course that would make Republicans look good, so...
It made no economic sense to feed, house, cloth and provide medical care for an investment that did not cash flow.
which explains the seceding states’ heated insistence on expanding slavery westward into the territories, I guess...