The percentage of total free families owning slaves in the Upper South had declined."
In 1860 slave populations in Maryland and Delaware were declining and in Missouri declining as a percent of the population.
One reason for declining slave numbers was increasing freed-black populations in those states.
Another was the continued rapid increase in slaves in the Deep Cotton South.
That increase was so great it changed the percent of Deep South slaves to total slaves from 50% in 1840 to 60% in 1860.
In 1860 both the numbers of slaves and market prices for slaves were increasing to all-time highs, due to the booming cotton economy.
So, bottom line, suggestions that slavery was dying out in Border South states might have some merit, except that in 1860 there was not even a breath of a hint of abolitionism in those states.
And one reason for slavery's relative decline in Border States was the booming demand for slaves in the Deep Cotton South.
It's no coincidence that in those Deep South states where slavery was most important, the 1860 election of "Ape" Lincoln's "Black Republicans" was enough to drive them to declare secession and war on the United States.
FLT-bird: "This is the same process that happened elsewhere as industrialization took hold."
And in the Northern US, but nowhere was the investment in slavery more important & rewarding than in the Deep South, and nowhere was resistance to abolition more intense.
- "Our position is thoroughly identified with the institution of slavery-- the greatest material interest of the world.
Its labor supplies the product which constitutes by far the largest and most important portions of commerce of the earth." -- Mississippi Reasons for Secession 1861