During the creation of the US constitution there was a debate over how, or even if slaves should be counted for purposes of representation. One hilariously insulting idea was the 2/3rds idea. The compromise that won over all the others was the sunset clause. The central idea was any one born on US soil after 1847 would be born free, with slavery dying a natural death.
How would america change as a country with out the sunset clause? Would free states try to block states from joining the union? Would the economy of the south be different? Would there be more slave revolts?
The Sunset Clause was kind of a double-edged sword; while it, sadly, did end up, in part, lead to the extension of slavery all the way up until 1912, it also did set up the idea that slavery would not be officially protected by the government-because of this, "Fire-Breathers", like John Calhoun, Robert Rhett, Clement Vallandigham, and Alexander Stephens, who advocated spreading slavery throughout the entire country, never gained much traction.
An interesting thought!
Would there be no Sunset Clause at all, or would there have been some other compromise instead? No Sunset Clause would, of course, mean the futile efforts to have it repealed via constitutional amendment in the 1830s would never have happened. And without it, we probably wouldn't have seen the South become as reliant on slave imports post-1847, since there would still be legal U.S.-born slaves.
How long could Chattel Slavery had lasted in the U.S. without the Sunset Clause?
In OTL we didn't see the Slave Trade banned in the United States until the 1880s and even then thanks to the way existing slaves were grandfathered in the last slave wasn't freed until 1912. And all that happened because by that point slavery had simply become an uncompetitive business model thanks to the compounded effects of the Sunset Clause reducing the American slave population coupled with the increased costs of imports. Most of the South had abolished slavery on its own by 1875, the Abolition Act just federalized what by then was inevitable.
Without that? I'm not sure. Most of the rest of the world had abolished slavery by the end of the 19th Century, so there's a good chance IMO that America would've followed suit by the 1880s or 1890s anyway. Then again, with how entrenched the practice was in this country, I wouldn't be shocked if it lasted well into the 20th Century.
Either way, industrialization will have killed slavery in America by no later than 1930, I think.
Without the Sunset Clause, why wouldn't chattel slavery become a permanent institution? Slavery in some form was seen as integral to the economy of the southern states, as demonstrated by their efforts to remove or circumvent the clause. There also will not be same societal pressure for abolition--without the Jubilee Generation, free black populations will be small and not very influential. Even international pressure may be diminished without the horrific excesses of the 19th century slave trade--I can't see Britain getting as worked up about a purely domestic American issue like that.
Slavery would not have become a permanent institution in America-in fact, if you remember, the Cotton Recession of 1870 was caused by slavery-related issues; even though slavery was well on the decline, the "Peculiar Institution" was still tied enough to the national economy that some problems developed up North as well-it was fairly mild compared to the Great Depression, but it still shook people up enough that the South was finally pressured into giving up slavery.
And with that, imagine what would have happened if slavery had managed to survive all the way into maybe the 1940s at the very most, and was actually protected by the U.S. government-the esteemed historian and economist Joseph J. Turtledove wrote a now fairly obscure but still interesting counterfactual story(
Dixie Domination, I think?) regarding such a scenario in 1977, utilizing his truly deep knowledge on both the subject of slavery and economics; needless to say, it all ended with an American economic implosion so massive that it made OTL's Great Depression of the '30s look like a cakewalk-the economics are fairly complex, and that I could not explain in person, but it is quite plausible(even if slavery lasting until the 1940s is not, nearly so much).