Lincoln was prepared to let the South go peacefully until they attacked a Union fort. That unified the country to fight overnight.
Pretty much. Lincoln repeatedly told his cabinet that they *could not* fire the first shot, and must wait to see if the South did. Sure enough, the slavers attacked Ft. Sumter.
Europe largely did away with slavery long before the US did because there was no shortage of farm labor in Europe and there was in the US. Slaves were originally imported to the US because of a labor shortage for large scale plantations which were common in the South. In the north smaller family farms were the norm and slavery was much less common even when it was legal there.
Industrialization was already beginning to make slavery uneconomical on the eve of the civil war.
Some economic analyses say that the cotton gin made slavery profitable again, because nobody knew how to automatically pick cotton yet. Slavery ended up being focused on cotton and sugar, mostly; crops where picking them had not been mechanized but processing had.
Because of the farm labor shortage in the north steam driven tractors and other farming aids became much more common in the north during the war. I have read that slavery might have been mostly dead from the changing market by the 1890s or 1900.
The plantation owner leadership would never have let it happen. I spent a while studying the lead-up to the Civil War; these plantiation owners were complete fanatics who believed that slavery was essential. They were trying to force slavery onto the free states and territories, and started right off with plans to invade the free states.They kidnapped free black people from the north to enslave them.
They were crazy. The reason appears to be that they derived their social status from having slaves, and without slaves, they lost their unearned social status. And if non-slavers could acheive similar wealth and power... they lost their social status. They were willing to set their own states on fire to preserve their social status. Of course, they wouldn't fight themselves; it was a "rich man's war and a poor man's fight"; they sent the poor whites to fight while relaxing in their plantations.
There's a reason Sherman said that 10% of the eldest sons of the plantation owners had to be killed in order to stop them. The plantation owners needed their spirits broken. Unfortunately, this didn't happen. If the Confederate generals, colonels, and "government" had all been executed for treason, things would have gone a lot better.
In fact, Lincoln, like most people in the North, would happily have allowed the country to be half slave and half free, but *the slavers would not let it happen* -- they kept insisting on forcing slavery into the free states, kidnapping free black people and enslaving them, et cetera. This was unacceptable to the North, obviously, but the slavers would not settle for anything less than total domination. Lincoln explains this in the Cooper Union speech.
After the Civil War, the plantation-owning slaver elite basically reinstituted near-slavery, using sharecropping, segregation, and the KKK; but *they didn't try to force it on the rest of the country*, and so the rest of the country shrugged its shoulders and let it happen.
The Civil War was actually over whether slavery would expand, or whether it would be contained. This is something very few people understand because great efforts have been made to cloud the topic, mostly by pro-slavery types. But it is very clear from the contemporaneous documents. It was contained.