I saw an interesting post about American slavery. It stated that if slaves had not been imported to America, they never would have been freed by Republicans and therefore enjoy freedom which blacks don't enjoy anywhere else on earth.
Slavery is an abomination. But in America, it served to free millions of black peoples from a life of poverty and economic outcast everywhere else on earth.
The evolution of this uplifting has taken 100 years and hasn't happened anywhere else on earth. That is the legacy of American slavery.