It would not have changed. Any rational person can see that slavery would have continued in the Union unchanged as it had been for "four score and seven years".
You are asserting that the illusion of change was the cause of the war. Of course they didn't expect a war, so it's hard to see how you can assert that even the illusion that slavery was threatened could have led to a war.
A rational thought, if they felt their economic underpinnings were threatened by the ideas of a Republican majority Congress and a Republican President.
It's hard to see how anyone could rationally have believed that. Firstly it was constitutionally impossible, and secondly both Lincoln and the Congress had offered them additional constitutional protections, which somehow didn't sway them at all.
There was no real potential of any changes to their system either in or out of the Union. This is why I point out that the claim the war was about slavery doesn't make any sense, and I have since come to regard it as just propaganda to justify what was done to them.
“I have since come to regard it as just propaganda to justify what was done to them” Much of that “propaganda” can be found in the excerpts of their secession ordnances. Don’t tell me. Tell them. They left the Union before Abraham Lincoln was sworn in as President. The operative word is “rational.”
If it's propaganda then a lot of Southerners fell for it.
"African slavery is the cornerstone of the industrial, social, and political fabric of the South; and whatever wars against it, wars against her very existence. Strike down the institution of African slavery and you reduce the South to depoulation and barbarism." - South Carolina Congressman Lawrence Keitt, 1860
"Our people have come to this on the question of slavery. I am willing, in that address to rest it upon that question. I think it is the great central point from which we are now proceeding, and I am not willing to divert the public attention from it." - Lawrence Keitt
"The triumphs of Christianity rest this very hour upon slavery; and slavery depends on the triumphs of the South... This war is the servant of slavery." - Rev John Wrightman, South Carolina, 1861.
"[Recruiting slaves into the army] is abolition doctrine ... the very doctrine which the war was commenced to put down." - Editorial, Jan 1865, North Carolina Standard
"What did we go to war for, if not to protect our [slave] property?" - CSA senator from Virgina, Robert Hunter, 1865
"I am not ashamed of having fought on the side of slavery—a soldier fights for his country—right or wrong—he is not responsible for the political merits of the course he fights in ... The South was my country." - John Singleton Mosby
"The vandals of the North . . . are determined to destroy slavery . . . We must all fight, and I choose to fight for southern rights and southern liberty." - [Lunsford Yandell, Jr. to Sally Yandell, April 22, 1861 in James M. McPherson, For Cause and Comrades: Why Men Fought in the Civil War, p. 20]
"A stand must be made for African slavery or it is forever lost." - William Grimball to Elizabeth Grimball, Nov. 20, 1860, Ibid.
"This country without slave labor would be completely worthless. We can only live & exist by that species of labor; and hence I am willing to fight for the last." - [William Nugent to Eleanor Nugent, Sept 7, 1863, Ibid., p. 107]
"Better, far better! endure all the horrors of civil war than to see the dusky sons of Ham leading the fair daughters of the South to the altar." - [William M. Thomson to Warner A. Thomson, Feb. 2, 1861, Ibid., p. 19]
"A captain in the 8th Alabama also vowed 'to fight forever, rather than submit to freeing negroes among us. . . . [We are fighting for] rights and property bequeathed to us by our ancestors.' " - [Elias Davis to Mrs. R. L. Lathan, Dec. 10, 1863 Ibid., p. 107]
"Even though he was tired of the war, wrote a Louisiana artilleryman in 1862, ' I never want to see the day when a negro is put on an equality with a white person. There is too many free [n-word]s. . . now to suit me, let alone having four millions.' " - [George Hamill Diary, March, 1862, Ibid., p. 109]
"A private in the 38th North Carolina, a yeoman farmer, vowed to show the Yankees ' that a white man is better than a [n-word].' " - [Jonas Bradshaw to Nancy Bradshaw, April 29, 1862 Ibid.]
"A farmer from the Shenandoah Valley informed his fiancée that he fought to assure 'a free white man's government instead of living under a black republican government.' " - [John G. Keyton to Mary Hilbert, Nov. 30, 1861, Ibid.]
"The son of another North Carolina dirt farmer said he would never stop fighting the Yankees, who were 'trying to force us to live as the colored race.' " - [Samuel Walsh to Louisa Proffitt, April 11, 1864, Ibid.]
"Some of the boys asked them what they were fighting for, and they answered, 'You Yanks want us to marry our daughters to the [n-word]s.' " - [Chauncey Cook to parents, May 10, 1864, Ibid.]
"An Arkansas captain was enraged by the idea that if the Yankees won, his 'sister, wife, and mother are to be given up to the embraces of their present dusky male servitors.' " -[Thomas Key, diary entry April 10, 1864, Ibid.]
"Another Arkansas soldier, a planter, wrote his wife that Lincoln not only wanted to free the slaves but also 'declares them entitled to all the rights and privileges as American citizens. So imagine your sweet little girls in the school room with a black wooly headed negro and have to treat them as their equal.' " - [William Wakefield Garner to Henrietta Garner, Jan 2, 1864, Ibid.]
"[If Atlanta and Richmond fell] we are irrevocably lost and not only will the negroes be free but . . . we will all be on a common level. . . . The negro who now waits on you will then be as free as you are & as insolent as she is ignorant.' " - [Allen D. Chandler to wife, July 7, 1864, Ibid.]
"The South had always been solid for slavery and when the quarrel about it resulted in a conflict of arms, those who had approved the policy of disunion took the pro-slavery side. It was perfectly logical to fight for slavery, if it was right to own slaves." [John S. Mosby, Mosby's Memoirs, p. 20]
'We have dissolved the Union chiefly because of the negro quarrel. Now, is there any man who wished to reproduce that strife among ourselves? And yet does not he, who wished the slave trade left for the action of Congress, see that he proposed to open a Pandora's box among us and to cause our political arena again to resound with this discussion. Had we left the question unsettled, we should, in my opinion, have sown broadcast the seeds of discord and death in our Constitution. I congratulate the country that the strife has been put to rest forever, and that American slavery is to stand before the world as it is, and on its own merits. We have now placed our domestic institution, and secured its rights unmistakably, in the Constitution; we have sought by no euphony to hide its name - we have called our negroes "slaves," and we have recognized and protected them as persons and our rights to them as property.'- Alabama Congressman Robert H. Smith, Source: http://books.google.com/books?id=zQ4wzvvk5dIC&pg=PA65&lpg=PA66
As the last and crowning act of insult and outrage upon the people of the South, the citizens of the Northern States, by overwhelming majorities, on the 6th day of November last, elected Abraham Lincoln and Hannibal Hamlin, President and Vice President of the United States. Whilst it may be admitted that the mere election of any man to the Presidency, is not, per se, a sufficient cause for a dissolution of the Union; yet, when the issues upon, and circumstances under which he was elected, are properly appreciated and understood, the question arises whether a due regard to the interest, honor, and safety of their citizens, in view of this and all the other antecedent wrongs and outrages, do not render it the imperative duty of the Southern States to resume the powers they have delegated to the Federal Government, and interpose their sovereignty for the protection of their citizens.
What, then are the circumstances under which, and the issues upon which he was elected? His own declarations, and the current history of the times, but too plainly indicate he was elected by a Northern sectional vote, against the most solemn warnings and protestations of the whole South. He stands forth as the representative of the fanaticism of the North, which, for the last quarter of a century, has been making war upon the South, her property, her civilization, her institutions, and her interests; as the representative of that party which overrides all Constitutional barriers, ignores the obligations of official oaths, and acknowledges allegiance to a higher law than the Constitution, striking down the sovereignty and equality of the States, and resting its claims to popular favor upon the one dogma, the Equality of the Races, white and black." -- Letter of S.F. Hale, Commissioner of Alabama to the State of Kentucky, to Gov. Magoffin of Kentucky
In the momentous step which our State has taken of dissolving its connection with the government of which we so long formed a part, it is but just that we should declare the prominent reasons which have induced our course.
Our position is thoroughly identified with the institution of slavery, the greatest material interest of the world. --Mississppi Declaration of the Causes of Secession
SIR: In obedience to your instructions I repaired to the seat of government of the State of Louisiana to confer with the Governor of that State and with the legislative department on the grave and important state of our political relations with the Federal Government, and the duty of the slave-holding States in the matter of their rights and honor, so menacingly involved in matters connected with the institution of African slavery. --Report from John Winston, Alabama's Secession Commissioner to Louisiana
This was the ground taken, gentlemen, not only by Mississippi, but by other slaveholding States, in view of the then threatened purpose, of a party founded upon the idea of unrelenting and eternal hostility to the institution of slavery, to take possession of the power of the Government and use it to our destruction. It cannot, therefore, be pretended that the Northern people did not have ample warning of the disastrous and fatal consequences that would follow the success of that party in the election, and impartial history will emblazon it to future generations, that it was their folly, their recklessness and their ambition, not ours, which shattered into pieces this great confederated Government, and destroyed this great temple of constitutional liberty which their ancestors and ours erected, in the hope that their descendants might together worship beneath its roof as long as time should last. -- Speech of Fulton Anderson to the Virginia Convention
Texas abandoned her separate national existence and consented to become one of the Confederated Union to promote her welfare, insure domestic tranquility and secure more substantially the blessings of peace and liberty to her people. She was received into the confederacy with her own constitution, under the guarantee of the federal constitution and the compact of annexation, that she should enjoy these blessings. She was received as a commonwealth holding, maintaining and protecting the institution known as negro slavery-- the servitude of the African to the white race within her limits-- a relation that had existed from the first settlement of her wilderness by the white race, and which her people intended should exist in all future time. -- Texas Declaration of the causes of secession
What was the reason that induced Georgia to take the step of secession? This reason may be summed up in one single proposition. It was a conviction, a deep conviction on the part of Georgia, that a separation from the North-was the only thing that could prevent the abolition of her slavery. -- Speech of Henry Benning to the Virginia Convention
Gentlemen, I see before me men who have observed all the records of human life, and many, perhaps, who have been chief actors in many of its gravest scenes, and I ask such men if in all their lore of human society they can offer an example like this? South Carolina has 300,000 whites, and 400,000 slaves. These 300,000 whites depend for their whole system of civilization on these 400,000 slaves. Twenty millions of people, with one of the strongest Governments on the face of the earth, decree the extermination of these 400,000 slaves, and then ask, is honor, is interest, is liberty, is right, is justice, is life, worth the struggle?
Gentlemen, I have thus very rapidly endeavored to group before you the causes which have produced the action of the people of South Carolina. -- Speech of John Preston to the Virginia Convention
This new union with Lincoln Black Republicans and free negroes, without slavery, or, slavery under our old constitutional bond of union, without Lincoln Black Republicans, or free negroes either, to molest us.
If we take the former, then submission to negro equality is our fate. if the latter, then secession is inevitable --- -- Address of William L. Harris of Mississippi
But I trust I may not be intrusive if I refer for a moment to the circumstances which prompted South Carolina in the act of her own immediate secession, in which some have charged a want of courtesy and respect for her Southern sister States. She had not been disturbed by discord or conflict in the recent canvass for president or vice-president of the United States. She had waited for the result in the calm apprehension that the Black Republican party would succeed. She had, within a year, invited her sister Southern States to a conference with her on our mutual impending danger. Her legislature was called in extra session to cast her vote for president and vice-president, through electors, of the United States and before they adjourned the telegraphic wires conveyed the intelligence that Lincoln was elected by a sectional vote, whose platform was that of the Black Republican party and whose policy was to be the abolition of slavery upon this continent and the elevation of our own slaves to equality with ourselves and our children, and coupled with all this was the act that, from our friends in our sister Southern States, we were urged in the most earnest terms to secede at once, and prepared as we were, with not a dissenting voice in the State, South Carolina struck the blow and we are now satisfied that none have struck too soon, for when we are now threatened with the sword and the bayonet by a Democratic administration for the exercise of this high and inalienable right, what might we meet under the dominion of such a party and such a president as Lincoln and his minions. -- Speech of John McQueen, the Secession Commissioner from South Carolina to Texas
History affords no example of a people who changed their government for more just or substantial reasons. Louisiana looks to the formation of a Southern confederacy to preserve the blessings of African slavery, and of the free institutions of the founders of the Federal Union, bequeathed to their posterity. -- Address of George Williamson, Commissioner from Louisiana to the Texas Secession Convention