Nonsense.
In fact, in March 1861 Lincoln offered to maintain peaceful relations and told secessionists they could not have war unless they themselves started it.
Lincoln was fully prepared to keep military "hands-off" the Confederacy.
But he was not going to let them grab whatever they wanted without consequences.
Jefferson Davis & company took Lincoln's words & actions as acts of war and so started (Fort Sumter) & formally declared war on the United States, May 6, 1861.
semantic: "It was always about preserving the Union, and not exactly the noble reasons espoused by Lincoln, et al.
Rather, it was simply a raw exercise in power, no different than GBs attempt at defeating the Revolution."
Of course it was about protecting the Union from Confederates' aggressive actions to destroy it.
But protecting slavery (Confederates) and freedom for slaves (Unionists) were never far from the top of the list of reasons for war.
To suggest otherwise is simply disingenuous.
You just admitted that the reasons besides protecting the union were secondary, as if they mattered in the end when they didn’t.
Fast forward 150 years and look at Catalonia which is trying to secede for purely economic reasons, and how many world leaders support them and/or would oppose the Spanish military keeping them in by force? Not many. In fact, I can’t think of one.