There is a virtual army of South hating freepers that would disagree with that. Legion.
The articles of Confederation explicitly created a perpetual union, stating that no “alteration at any time hereafter be made in any of them; unless such alteration be agreed to in a Congress of the United States, and be afterwards confirmed by the legislatures of every State”.
That said, the war didn’t start because Lincoln wanted to preserve the Union, though he certainly did.
The war started because the radicals in South Carolina thought they needed war.
Remember, prior to the attack on Fort Sumter, only seven states had seceded. Arkansas, Delaware, Kentucky, Maryland, Missouri, North Carolina, Tennessee, Virginia had not.
Virginia had the largest population, most of the shipping, and the only industry in the South. A seven-state Confederacy would have been a poor backwater, easily dominated by both the US and the European powers.
At the time of the attack on Sumter, there was a debate going on in Congress over what to do. Yes, some were calling for war, others were calling for peaceable recognition. Had Congress recognized the secession, which it was very likely to do, Lincoln would have had little recourse.
Lincoln may have wanted war, but the thing is, so did South Carolina. They thought that only war would convince the other eight slave states to join the secession. They saw themselves with a choice between peace and a seven-state Confederacy or war and a fifteen-state Confederacy. So they rushed into war, trying to preempt any effort in Congress to recognize the secession. (And got an eleven-state Confederacy - and that only for four years. So it goes.)
I am not one but I am the first in my family since 1776 and before to live in one of the States of the Rebellion. My wife’s history major was practically The Civil War and she has written long papers and can talk quite a while on it and for every thing I can come up with that is “new” to me she can jump in a take off with footnotes and references. SHE can’t give a satisfactory answer on why that war took place. I doubt any of the folks who survived could. Come to think of it I doubt any soldier in any war has really understood anywhere near fully just why they are there. Slavery was the moral motivator that got the Union soldiers to fight, no question. How important was it? Lincoln himself said that if it preserved the Union he would not free a single slave so it must not have been all that important, at least to him.
Why? I don’t think anyone knows. There were many reasons and none good but together they must have been enough because it pretty much undeniably happened. The home in which I sit is surrounded with trenches and excavations that stand as mute testament to the fact that there was, indeed, a war around here.
The Federalist Papers are quite informative about how secession and accession are both plausible. The Committee on Style made some changes to the preamble that confused the issue of whether the States or the people joined the Union. Salmon Chase preferred amnesty to the former Confederates and stated that if secession was tried in a court of law he didn’t think the Union would win and would have to pay reparations to the South.
IIRC, every secessionist state held a convention to decide the matter. IOW, they left the Union in the same fashion as they entered, through the convention process. This was in perfect accordance with our founding principles.