Still, violence has been the answer in many (most?) political revolutions, including the American revolution and separation from Britain.
The Confederacy tried to replace their Constitutional government and the policies instituted by the leaders elected by the people with a violence-enforced new state inside the territory of their existing one and got (justifiably) multi-generationally brutalized for their trouble. The town I grew up in and moved away from was still raising funds to rebuild some of the places that were burned to the ground in the war. That was fundraising in the 1980s.
Every time someone points to the 1776 war as a success story I feel compelled to point out that half the descendants of that war's victors tried a very similar thing in 1861 to absolutely ruinous result.
(On this topic: Fort Sumter is an interesting story. While it was never taken during the war, it basically became a target-practice and weapons field-test location for the Union navy: every time they had a new technique or a new cannon they wanted to try out, they'd try it on the fort. By the end of the war, the fort was "standing" only in the sense that the bulk of its above-ground works had been blasted flat and were shoved together into an earthworks bunker; the Confederates were basically sheltering in a hole that a lobbed shell could fall into at any time.
And while the fort and its northways sister kept Union ships out of the harbor, it didn't stop them from firing past the fort into Charleston itself, since "war crimes" and "civilian populations" weren't really a concept yet.
People very much went into that war thinking there wouldn't be consequences for ordinary folk. They were very much wrong.)
Once that happened, it really wasn't up to Congress or the President any longer. The capture of Fort Sumter and declaration of succession moved the conversation from "How much slavery can America tolerate" to "this insurgent government has stolen half of the country's territory." The response to that threat was as self-evident as it would have been if that territory had been taken by another existing nation.
It is strange to me that you take such a fatalistic approach to history, where nothing else was ever possible.
of course at some point there is no turning back, particularly after the deed is done.
If nothing else is possible, what does that say about the current state and our choices about our future? what will be will be? might as well stay home watching netflix and see what happens?
If we want to turn the stories of the past into questions about what we could do differently right now, that's an interesting conversation to me. "But what if the South had just decided not to get into a shooting war with the North?" is fodder for a stack of books on the "New Fiction" table at Barnes and Noble but not much more.
Turning the lens to the present: I think it is worth noting that decades of negotiation, political horse-trading, and compromises had been attempted prior to the breakout of the War. It isn't that talking wasn't tried, it's that one side got tired of having the conversation every single generation (and were perceiving that the zeitgeist were turning against their position). So one useful question is "What are the divisions in this era that mirror the kind of irreconcilable difference that was 'a nation half-slave and half-free?'" One candidate I could suggest is the question of gun control; I suspect it is not, as practiced in the US, a topic where people can agree to disagree, the Constitutional protection (and judicial interpretation of it) distorts the entire conversation, and I think there's real nonzero risk of one side responding to a sea-change in the zeitgeist conversation with violence.
Which side, I do not yet predict. A major ingredient in the slavery debate was existential fear (the belief in the South that a freed black population would form either a power bloc that would destroy its former masters politically or vigilante posses that would do violence to their former masters). It's one of the reasons John Brown's raid was so terrifying to the Southerners because Brown was a white man who committed political violence in the name of ending slavery; they perceived him as a signal that the North was done talking (even though he was not acting as an agent of the government). In modern America? A lot of Americans are terrified of random gun violence. That kind of terror lowers the bar on willingness to commit violence, because the survival drive runs hot. And, similarly, gun owners are terrified that the government could strip their capacity for self-defense from them and they'd then be vulnerable to violence they could not defend themselves from.
If you're looking for a lesson from the past on how to diffuse such a volatile situation... Unfortunately, I don't think the story of the Civil War will give it to you. That's a story of failing to diffuse it.