I thought the slave states were significantly poorer than the free states, a major advantage of the North in the Civil War? I'm sure it's been examined, but would the South have been better off with paid labor of free people? Countries using that model do far better. Imagine someone trying to compete with slave labor against a modern enterprise.
For colonization, that seems to have played a minor role in the US economy?
My understanding of the pre-industrial or non-industrial US economy is that it's most powerful engine was the Mississippi River basin, which is something like the largest continguous amount of farmland in the world with navigable waterway access to the sea (and thus a way to get goods to market, as overland transport was much too expensive - compare a barge to a horse, or even a train).
I believe that's at the heart of the Civil War discussion, because downstream of that mythology, alongside the "life and liberty" parts, are the compromises of slave vs free states. What took place from the founding into the 19th century was the experiment in following the myth and seeing where it led, which favored industrialization. The South had the wealth when the nation was agrarian, but the founding principles gave a political edge to industrialists, enabling the development of roads, canals, and eventually rails, while also using cheaper immigrant labor to build those things; using slaves to do these projects creates a less favorable balance sheet for the owner, because bodies that you own and are mandated to take responsibility for cannot simply be fired and replaced with new ones if they are too weak to work.
This tension of old vs new wealth also propelled western expansion, since it led to the "1 free state per slave state" dynamic to maintain political consensus, only for it to hit an abrupt ending in the 1850's when expansion reached the West Coast.
The 'mythology' is an attempt to dismiss it - ironically using Enlightenment concepts. The Enlightenment was the escape from mythology, using actual fact and reason, which is the foundation of democracy.
Much more than mythology, democracy, the US, and the Enlightment generally have been overwhelming successes in reality. Nothing in the history of humanity comes close.
The 'mythology' is that somehow dictatorship is somehow 'natural' or necessary or inevitable or even reasonable.