From the Northern side easily the most oft-stated reason for war, including from the President, was to preserve the Union.
Pray tell what you think "...preserve the Union" means if it doesn't mean drafting large armies, invading heretofore sovereign states, bringing devastation on their populations, and forcing them to remain as vassals to a centralized national government?
I know "Saving the Union" sounds a lot better, but it is what it is.
