Why did the South secede to preserve slavery? Slavery where it existed was not threatened. All the South had to do was agree to the Corwin Amendment and slavery where it existed would have been untouchable by constitutional amendment. Also, by seceding, the South gave up their constitutional right to the territories. How did secession protect what was never in question? They lost more rights by secession. There was no longer fugitive slave law and they lost their right to the territories. They lost more than they gained in protection of slavery.
you are caught up in the good v bad smokescreen. You want to believe that the United States would only declare war for virtuous reasons. That’s just not the case.
staying in the Union meant millions lost by the South. Secession meant millions lost by the North.
it’s very simple, follow the money.