Please note that my comment predicted a very slow death of the institution of slavery, although perhaps faster than the death of the abusive conditions in post-war Dixie. But your post is very interesting, and made me research further.
Your passage states that “In the decades before 1860, Deep South cotton production doubled, and doubled again, while cotton prices rose much faster than inflation — even including Federal import tariffs.”
I find this assertion about prices flatly contradicted by the data I can find. While production increased sharply, prices were very stagnant, having collapsed prior to 1830 and remaining quite low until the Civil War created a shortage.
I wonder if perhaps you are falsely figuring that an increase in demand of slaves means that slave plantations must be thriving? If the price of labor is booming, and the price of a product is so stagnant, then perhaps the death of slavery would have been coming faster than I foresaw it. The population of slaves in the decade prior to the Civil War increased 23%, compared to an overall population growth of 36%. This means that supply wasn’t keeping up with demand, resulting in higher labor costs, resulting in LOWER profits.
The bulk of the population growth in the US you cite was in the north, driven by European immigrants, very few of whom were attracted to the south because of the lack of opportunity there. The southern white population growth was much smaller. For example, between 1850 and 1860, Mississippi’s white population grew by 58,000 while it’s slave population grew by 126,000.
I plead guilty to quoting numbers from memory, never a good practice, so don't anybody else do it. ;-)
But since you asked, I'll quote you the actual numbers from page 21 of the book referenced above:
"So too, in the 1850s compared to the 1840s, the Sea Island cotton crop increased 200 percent in value, the sugar crop 150 percent, and the tobacco crop 67 percent.
In comfortable contrast, the southern cost of living during the 1850s eased up less than 33 percent.
"Only those politically crucial gentlemen, South Carolina rice planters, still suffered under dreary economic skies.
These squire's debts had multiplied faster than their assets even in the 1820s, when rice yields and prices had remained more immune than cotton figures from the worldwide economic downturn.
In the 1850s, rice planters' immunity from market caprices and soil exhaustion ended...
"...Southerners developed almost 30,000,000 previously untouched acres during the 1850s, increasing the land under cultivation by over a third.
Southern farmland doubled in value during the decade, southern railroad lines more than tripled in length, and southern industrial receipts swelled 67 percent.
[Yes] Compared to the North, the South remained poorly developed industrially and ill connected by railroads.
But in the late 1850s, the rate of new development in Dixie surpassed Yankee standards.
"In one area, the South set records than Yankees scorned.
The price of slaves took off in the 1850s.
The average price for a Lower South slave, after hovering around $925 from 1830 to 1850, averaged $1,240 in 1851-55 and $1,658 in 1856-60, a 79 percent rise in the South's largest capital investment.
"After the national Panic of 1857, when the North fell into prolonged depression and the South quickly recovered, Southerners gloated about getting rich quicker than money-mad Yankees."
So, quoting those figures from memory, I don't think I did so badly, certainly getting the gist it correct -- in 1860 the Deep South was booming economically like never before, or since.
This is reflected in every important economic number from that period.
The population of slaves was confined entirely to the Southern states. That 23% increase was very significant in states that saw very little in the way of new immigrants.
The overall 38% population growth was for the entire nation and spurred by immigration from Europe, primarily Ireland and the German states, and that immigrant population was primarily concentrated in Northern states.
The South was becoming short on new lands for plantations (and the needs for slave labor) while the North was looking for new lands for single family farms for the new immigrants.
Hence, the conflicts over Homesteading, Dred Scott, the Kansas-Nebraska Act and the expansion of slavery to the Western territories.
It wasn't slavery per se that caused the Civil War... it was the conflict over the expansion of slavery that caused it. In other words, who would win the West. Freemen or Slavery.