That's what I said, though I'm not sure how you figure they mushroomed up to 3.5 million so fast.
1808 to 1860. The 1860 census listed over 3.5 million slaves in the United States. The year 1807 was the last year that slaves could be legally brought into the United States. The Delta is from the birth rate of slaves in the country. I am sure that because the slave trade was outlawed, does not mean that all importation of slaves ceased, but the vast majority of slaves in this country by 1860 were born here.