Would a Civil War have broken out had the states not ratified the 13th amendment, also known as the Corwin Amendment?
That's a good question.....though it would have been for the better had the Corwin Amendment not come to pass, even if a Civil War had occurred(as tragic as
that would be). Because we likely would have avoided not only the humiliations of the 1880s, or the Panic of 1898, but also the domestic tragedies of the first decade of the 20th Century(like the Ellis Island bombing of 1908 which killed 284 people and injured many hundreds more, just weeks before the Corwin Amendment was repealed), too, as well as the horrendous street-level bloodbaths that followed the decade after(and did not stop with our entry into the Great War in 1913, nor end after it's conclusion in 1915-16), as reactionaries and radical progressives fought each other nearly every day of the week somewhere in the country.
Granted, the good guys ultimately won, but not before some 150,000 innocent lives had been claimed by political violence by 1919(and that's going by official U.S. gov't statistics that don't include lynchings, of which at least 18,000 are known to have occurred between 1860 and 1908, half of them African-Americans, including a few thousand enslaved). And so much of that can be traced, sometimes directly, sometimes indirectly, right back to the Corwin Amendment. I can only be thankful that we learned our lesson, even if rather late.....
OOC: TBH, I really don't think the Corwin Amendment could have succeeded with a POD after 1859-60; anti-slavery sentiment was just too strong in too many of the states north of the Mason-Dixon at that time IOTL. Maybe something closer to, say, 1854-55 might work?