They were used in cattle ranching and hog husbandry. They worked as butchers and meat processors. In places like the Chesapeake Bay region enslaved individuals were involved in oyster harvesting and processing.
[1] https://en.wikipedia.org/wiki/Albion's_Seed
[2] This is why the framers fabricated a notion of "White" identity, to create solidarity where none had really existed. To understand what they meant by race one must look at contemporary dictionaries. Needless to say the word meant something very different over 200 years ago than it does today.
Slavery didn't build the U.S. The mostly-slavery-free North built the U.S.
It may not have harboured slaves, but it was definitely profiting by them.
And early stages of industrialisation, most notably the cotton gin, extended the viability of slave-based plantation labour by several more decades, according to extensive accounts.
The Southerners had expected that they had a trump card with cotton exports to the North, but oops.
The South languished in part due to Reconstruction and being politically repressed by the North following the Civil War, but also for geographic and climatic reasons: it was hot and humid, and would remain hot and humid until electrification and air conditioning arrived ~1930--1950, the oil booms of Texas, Oklahoman, and Louisiana (~1900 -- 1940), and arrival of petrochemical industry (1950--).
Agreed that cotton was a ... weaker thread ... binding South and North than the South would have hoped for.
And whilst we're talking regional economic development, though an unrelated territory: I found it interesting a while back to find that Los Angeles in the mid-20th century was often the second-largest manufacuturing centre across a whole slew of industries: oil, automobiles, aircraft, tyres, among them. I've yet to find a good explanation of this, though my own hunch is that it was a combination of factors:
- Local petroleum sources, that is, a tremendous energy supply.
- Far enough from East Coast manufacturing that a local industry made sense.
- A sufficiently large local population to feed that demand.
This pattern emerged after the Great Earthquake and Fire of 1906 in San Francisco which greatly dampened development of Northern California, as well as the Bay Area's geographic limitations (a small peninsula, poor cross-bay transport until the creation of the Golden Gate and SF-Oakland Bay bridges in the 1930s), as well as a largely agricultural / timber orientation of Northern California's economy, with secondary strengths in transportation (ports, railroads) and finance.
The timing was such that it was too late for the South to be able to win independence -- the North was already too strong. But when the North was weaker the drive to secession was also weaker because the resentments were bred in part by the stark contrast in prosperity. The North had to get strong enough to win the war for the South to be willing to go or endure the war.
Sam Houston understood all of this, and for his troubles of advising Texas stay in the Union he was removed as governor by the legislature.