There are more slaves in the United States (estimated) than there were at the beginning of its Civil War.
This doesn't check out from what I found.
In 1790, the first census of the United States counted 697,624 slaves. In 1860, the eighth census counted 3,953,760.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7716878/
Modern slavery in United States Estimated number living in modern slavery: 1,091,000 (3.3 per thousand)
https://www.walkfree.org/global-slavery-index/country-studies/united-states/
Seems like today's count is a little more than 1/4 of the count from right before the Civil War. It's still a huge number. They're both devastating stats. What source do you have that puts today's number bigger?
That makes sense.