" The South’s 1860 population of 3,953,742 enslaved people comprised or made viable an estimated four billion dollars’ worth of private property...
...Four billion dollars was more than double the $1.92 billion value of farmland in the eleven states that seceded.* Without labor Southern land lost what value it had, but even with labor Southern land in 1860 still was worth much less than land in the free states "

― Ned Sublette , The American Slave Coast: A History of the Slave-Breeding Industry