I’ve often read and heard that many of the founders just assumed the institution of slavery would eventually just fade away and die out, but the invention of the cotton gin made slavery an integral role in the Southern Economy.
However I was reading some statistics on slavery populations and it appears that the proportion of the population in slavery in 1800 was actually greater than the proportion in 1860, which made me question the argument argument above.
While more can always be written, you may be interested in this comment of mine from the other day. The short answer is, no, slavery was not on its way out. Slavery was very profitable without cotton, and many of the slave states never engaged in the cotton industry in any widespread fashion, yet slavery remained immensely profitable there. What cotton did do was provide the most profitable industry in some of the slave states. But had cotton not emerged to be as profitable as it did, there were many other avenues to profit that slaveholders could have engaged in instead. And with almost certainty, they would have done so. Rather than give up slavery, slaveholders would have found something else to force the enslaved people to do.