Show me how. The Civil War was a horrible thing, but it was took place because the South’s reaction to an electoral defeat was not “We have lost, we’ll try again in 1864”, but “Well, since we don’t have power, we’re out. Oh, and we’re taking the forts built with federal money with us.” How would a divided nation have been better?
Oh! You decided to employ the irritating tactic of condescension! Now I see where you are coming from.
I can argue Abraham Lincoln’s motives all day long, but there’s no point in doing that, because I’ve been through this many times before-I’ll produce my evidence, you’ll produce the few quotes that get used every time totally stripped of any context and place, ignore any refutations of them, and we’ll go around in circles.
So let’s just talk about results-when he was shot on Good Friday 1865, he had dealt a mortal blow to slavery, watched the House of Representatives pass the 13th Amendment (a key plank in his 1864 re-election platform), and ensured that the nation wouldn’t be split apart. He had also given the remarkably powerful Second Inaugural and even a speech advocating for black suffrage.
Now, had Lincoln let the Southern States go, there would be no movement towards abolition (in fact, in most Southern states, any mention of the possibility of abolition was outright illegal; even Kentucky ran out Cassius Clay), there would be two nations rather than one, and a hostile border running the length of the continent. How is that better?