The 1860 census counted just over 4 million enslaved African Americans in the South, out of a population of about 31.4 million.[0][1]
There are about 1.9 million people incarcerated in jail or prison in the United States today.[2]
The scale of incarceration in the US today is mind-boggling, but is itself under half the number of people enslaved at the height of the Southern slave economy.
[0]https://usafacts.org/articles/the-1860-census-counted-4-mill... [1]https://www.census.gov/library/publications/1864/dec/1860a.h... [2]https://www.prisonpolicy.org/reports/pie2023.html
The oddness of referring to the "slave trade" is the height of the "Atlantic Slave Trade" far predated the peak of slavery in the US and contributed directly far more to the Caribbean and Brazil than to the rest of the Americas. US chattel slavery, particularly the form that exploded post cotton-gin, was a system of directly controlling the reproductive capacity of enslaved black and native Americans.