So this is... I won't say my favorite topic... but it is one which I have given quite a bit of attention to in past threads. I would point you to this thread on Southern motivations and this one on Confederate Emancipation "plans", but the main one I would direct you to is this answer more broadly looking at Slavery as the underlying cause of disunion and civil war. As it is archived, I'll repost the whole thing here and am happy to handle follow-ups best that I can. I will additionally note that specifically whether Andrew Jackson being a ~90 year old President c. 1860 would have prevented Civil War is far too hypothetical to take a stab at, given the 'No What If' Rule.

I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so.

-Abe Lincoln's First Inaugural Address, March 4, 1861

It is a canard of Confederate apologia that war aims must be perfectly opposite. It is simply a fact that in his public statements, President Lincoln made clear that he was not out to abolish slavery, and that the Union undertook its campaign to prevent southern secession, since, in his words, the Union was perpetual, that "Perpetuity is implied, if not expressed, in the fundamental law of all national governments". So, their logic goes however, that if the Union did not launch its war to end slavery, then slavery was not the cause of the war. Nothing could be further from the truth. This work will attack this position from multiple angles, demonstrating not only that the protection of slavery was a principal aim of southern secession, but that the mere right to secede was never a clearly established legal one, at best subject to major debate, and indeed, only entering the national discussion as slavery became a more and more divisive issue for the young nation, and further, that aside from legal/Constitutional concerns, secession as performed by the South was an immoral and illiberal act.

Descending from these general principles, we find the proposition that in legal contemplation the Union is perpetual confirmed by the history of the Union itself. The Union is much older than the Constitution. It was formed, in fact, by the Articles of Association in 1774. It was matured and continued by the Declaration of Independence in 1776. It was further matured, and the faith of all the then thirteen States expressly plighted and engaged that it should be perpetual, by the Articles of Confederation in 1778. And finally, in 1787, one of the declared objects for ordaining and establishing the Constitution was "to form a more perfect Union."

-Abe Lincoln, March 4, 1861

The idea, often pithily expressed by the factoid of "The United States are vs. The United States is", that as originally envisioned the several states were essentially independent nations held together by a weak Federal entity for the common defense, and that it was the Civil War which changed this relationship, is an utterly false one. While Lincoln is perhaps a biased figure to appeal to, his observation nevertheless points to the sentiments of the Articles of Confederation, and the Constitution that followed, which speak of perpetuity and union at the time of founding.

At the time of drafting, James Madison, the "father" of the Constitution, noted in a letter to Alexander Hamilton that "the Constitution requires an adoption in toto, and for ever", because "compacts must be reciprocal". Likewise, while reading out the letter to the New York Ratification Convention, Hamilton expressed similar sentiment in response, that "a reservation of a right to withdraw […] was inconsistent with the Constitution, and was no ratification." Similarly, Washington, serving as President of the Constitutional Convention, noted "In all our deliberations on this subject [the perpetuity of the government] we kept constantly in our view that which appears to us the greatest interest of every true American, the consolidation of our Union, in which is involved our prosperity, felicity, safety, perhaps our national existence".^1 While it is certainly true that the Constitution made no explicit mention either way as to the correctness of secession, and that some expressed trepidation at the thought secession could not be an option, it is equally true that the issue was addressed at the time of ratification, and it was anti-secession Federalists such as Hamilton and Madison, with clarity of their position, who shepherded it through.^2

But if secession was not a clearly reserved right from the beginning, when did it begin to enter the "conversation"? Well, the fact of the matter is that the importance of the aforementioned perspective is itself a product of the post-war revisionist works. It is misleading at best to speak of state loyalties above country and in fact, it is demonstrable that it was the supremacy of national loyalties that helped to delay the divisiveness of slavery that started to nose itself into the national conscious with the 1819 Missouri Crisis^3a. Rather than being an inherent weakness of the Federal government as created by the Constitution, the apparent weakness of the Federal government was a creation of southern politicians specifically working to protect their slavery based interests from the mid-to-late 1820s on-wards, forcing compromises that maintained a balance between slave and free states. To quote Donald Ratcliffe:

The strengthening of national power in the 1860s reflected, in part, the restoration of the political situation that had existed before the South began to impose its deadening hand on the Union in the thirty years before the war.^3a

Now, while demonstrating that the doctrine of states' rights was not a constant over the first 80 years of United States politics, it still stands to show that, far from being a "flavor of the month", as some 'lesser' apologists assert, slavery was an absolute central component of Confederate war aims, and the defense of their 'peculiar institution' surpassed any principled defense of States' Rights. The simple fact of the matter is, that far from simply asserting their moral right to own another human being for the use of their labor, the southern states' need for slaves was intimately tied to their political and economic fortunes, to the point that any claim of political or economic reasons for secession can not be separated from the root base of slavery.

When Lincoln was elected in the fall of 1860, the South was terrified. Whatever his prior declarations that whether he wished to or not, he had no power to interfere with the institution where it existed, Lincoln was nevertheless a Republican, a political party founded on its opposition to slavery, and at its most mild, committed to stemming the further spread as statehood spread westward. While committed, absolute abolitionism was a vocal minority on the national stage, the simple limiting of expansion presented a long term existential crisis to the slaveholding states. Every free state to enter the Union represented additional Senators and Representatives to immediately exercise power in Congress, and represented the growth of power not only in future Presidential elections, where anti-slavery parties could continue to gain momentum, but in the long term even foreshadowed, one day, a strong enough majority to abolish the institution once and for all through Constitutional Amendment. And it wasn't only that Lincoln and the speedy rise of the Republican party threatened a political threat to slavery, but also that, due to the 3/5 Compromise, the existence of enslaved populations represented a significant boost to the electoral power of the slave states.^3b

Economically, the fortunes and viability of the South were intertwined with slavery so closely as to be inseparable. Turning to the Nullification Crisis of the 1830s, Calhoun observed that slavery was the undercurrent of economic disagreements with the northern states, although he was by no means the first or last:

I consider the tariff act as the occasion, rather than the real cause of the present unhappy state of things. The truth can no longer be disguised, that the peculiar domestic institution of the Southern States and the consequent direction which that and her soil have given to her industry, has placed them in regard to taxation and appropriations in opposite relation to the majority of the Union, against the danger of which, if there be no protective power in the reserved rights of the states they must in the end be forced to rebel, or, submit to have their paramount interests sacrificed, their domestic institutions subordinated by Colonization and other schemes, and themselves and children reduced to wretchedness.

While fears over the continued viability slavery had been a driving concern for southern politicians for at least a decade by then, it was the Nullification Crisis that clearly established the unbreakable ties of slavery and economic concerns. To quote Richard Latner:

South Carolina's protest against the tariffs of 1828 and 1832 was only a surface manifestation of profound planter fears, real and imaginary, that a hostile northern majority would subvert their slave system. The crisis laid bare southern anxieties about maintaining slavery and evidenced a determination to devise barriers against encroachments on southern rights.^4

I'm going to do my best to keep this answer political-neutral for the sake of a reasoned, civilized discussion on this...except to say that this rambling quote from Trump is astonishing in its demonstration of a non-existent grasp on even the basics of American history.

First, the Jackson stuff. To claim that Jackson had "a big heart" is at best an exaggeration, and at worst, an outright lie. There's no shortage of first-hand accounts detailing how cagey, vindictive, hot-tempered, and cruel the man was. His refusal to abide by the Supreme Court's decision on Worcester v. Georgia laid the groundwork for the Trail of Tears (though to be fair, Van Buren was in office by that time), and represents one of the cruelest, most regrettable moments in American history. It's understandable that Trump would respect/admire Jackson since the latter man operated with a "damn the torpedoes" style of governance, and stretched the bounds of executive authority (so in other words, he tried to serve as president with the authority of an unchecked king). I say "understandable" because in light of Trump's recent statements about abolishing the 9th circuit, and bypassing Congress to pass whatever legislation he wants, Trump seems to want to serve as president in much the same way.

But beyond the "big heart" comment, one has to scratch their head at whatever the hell Trump meant by stating that Jackson saw what was happening with the Civil War and felt "angry" and entertained thoughts of "there's no reason for this." I can't even begin to wrap my head around what Trump meant there. The Civil War started 16 years AFTER Jackson died, and the big 19th century event that most historians agree kicked off renewed debate about the Civil War, the Mexican American War, started a year after Jackson died. By this, I mean that the Mexican American War jump-started the abolition debate when arguments arose over how Texas would be admitted to the Union (as a slave state or free state). While the origins of the Civil War had been festering since the drafting of the Constitution (over slavery, big vs. small government, and the national bank), the Missouri Compromise put the discussion on the shelf for a bit. This Missouri Compromise happened before Jackson's term as president, and represented a delaying tactic by U.S. legislators and then-president Monroe to appease both the abolition and anti-abolition movements so that neither side had a clear advantage when it came to admitting new states to the union. The Mexican American War threw this balance into the air, however, as it opened the door to new states coming into the union in the south (which would skew the balance towards anti-abolitionists).

So you've got the Missouri Compromise before Jackson's presidency, which actually quieted the secession talk for a time, and kept the peace. Why would Jackson have stepped in to muddy the waters when president? There was no real, impending threat of secession since the Missouri Compromise had cooled those tensions some years before, so what should he have done? (In other words, there was no real threat of a Civil War at that time, just simmering tensions that no one really thought would blow up any time soon). And then after the Mexican American War, when those tensions DID begin to flare up, Jackson was already dead. So what would Trump have the guy do in that situation?

Now, as far as the bigger question: why was there a Civil War? There's no shortage of discussions on this sub that do deep dives into this very topic. Check out:

https://www.reddit.com/r/AskHistorians/comments/5kr3g4/why_did_a_lot_of_southerners_believe_that_the/

https://www.reddit.com/r/AskHistorians/comments/3edss0/was_the_american_civil_war_about_more_than_just/cte2mj9/

https://www.reddit.com/r/AskHistorians/comments/svoo6/causes_of_the_american_civil_war/c4hebtj/

TD;LR on that whole "why did we have a Civil War" question: it was a conflict that had its roots in the very founding of the nation, with arguments over big vs. small government, but more than anything else, slavery. There was a bitter, mortal struggle over the question of slavery in the United States from the get-go, and despite many MANY attempts to compromise, negotiate, and/or reason with each other, by 1860 and the election of Lincoln, things had reached a boiling point. Despite overtures from both sides (the south just wanted to be left alone to form their own government(s) and the north was no less determined to keep them in a single union), there was no way around it: there had to be a fight to settle things. The south would broker no terms except self-governance and separation, and the north under Lincoln would accept nothing short of a continued union under one nation. There was no more room for negotiation or understanding once the states began to secede. It's not like they asked permission to do this, or held out with an ultimatum, they just did it, leaving no room for compromise except to let them separate.

Lastly, to counter Trump's assertion that "people don't ask that question" about why there was a Civil War. Like many things that Trump says: that is an outright lie. People ask that question ALL. THE. TIME. It is the basis for most of the historiography on the topic, and a frequent topic of discussion in this very sub. It wasn't "worked out" because after 80+ years of arguing, the Confederate states just went ahead and broke off.

[Sources - Bruce Catton, 'Mr. Lincoln's Army'; Doris Kearns Goodwin, 'Team of Rivals'; Jaw Winik, 'April, 1865'; James McPherson, 'Battle Cry of Freedom']

I'l just put this here:

Causes of the American Civil War? by /u/Borimi

Civil War: Slavery or States Rights?

[Was the American Civil War about more than just slavery? by /u/Georgy_K_Zhukov] (https://www.reddit.com/r/AskHistorians/comments/3edss0/was_the_american_civil_war_about_more_than_just/cte2mj9/?st=j26fmgh7&sh=1b974f2c)

To think about this question, I would like to focus on the political debates that were being had at the time. In the North you have Abolitionists, and more centrist ideas about slavery. While some like William Lloyd Garrison had more radical arguments about full enfranchisement, others like Frederick Douglass had moral arguments about the hypocrisy of the institution of slavery.

The real disconnect comes from the South and proponents of slavery. You have a prominent figure in John C. Calhoun fighting for the state's rights to hold slaves. Calhoun argues that the North, the more populated area of the country, will soon hold mob rule over the South and take away their 10th Amendment rights.

"But as there can be no constitution without the negative power, and no negative power without the concurrent majority-it follows, necessarily, that where the numerical majority has the sole control of government, there can be no constitution; as constitution implies limitation or restriction- and, of course, is inconsistent with the idea of sole or exclusive power" - John C. Calhoun, “A Disquisition on Government (1848),” in American Political Thought (New York: W.W. Norton & Company, Inc., 2009), 615.

In this Calhoun is saying two things: 1) The numerical majority that the North has is not reason enough, in our constitutional government, to justify abolition. 2) That if abolition comes as a result of a numerical majority, then the Constitution of the United States is null and void, as government would no longer have restrictions. All law would be a result of the "tyranny of the majority"

Calhoun plays on a history of political debates that have been had since the advent of Classic Liberalism. Calhoun's idea that government needs to be restricted, to protect a minority from losing its voice, is not an uncommon one in American history.

Calhoun and many other prominent Southerners saw this as the principle issue of their time, and vowed to break up the Union rather than give up their slave economy.

"Resolved, That the union of the States rests on a equality of rights and advantages among its members; and that whatever destroys that equality, tends to destroy they Union itself..." - John C. Calhoun, “A Disquisition on Government (1848),” in American Political Thought (New York: W.W. Norton & Company, Inc., 2009), 605-606.

Thus, you had a stalemate between the two factions, where each believes more in their cause (Abolition or Slavery) than to protect the United States.

When Abraham Lincoln comes on the scene, his stance is more centrist. While he does admit that slavery may be a moral wrong, he acknowledges the Southern states' Constitutional rights to hold slaves. However, as time goes on and he grows more in his moral and Republican principals, he begins to side with Abolitionists.

"Remembering too, that the Jefferson party were formed upon their supposed superior devotion to personal rights of men, hold the rights of property to be secondary only..." - Abraham Lincoln, “Letter to Boston Republicans (1859),” in American Political Thought (New York: W.W. Norton & Company, Inc., 2009), 661.)

Lincoln, however, understood the volatile nature of the situation, and knew that both sides were willing to implode the Union to get their way.

Lincoln, on the Kansas Nebraska Act: "It is an aggravation, rather, of the one thing that ever endangers the Union." - Abraham Lincoln, “Speech at Peoria, Illinois (1854),” in American Political Thought (New York: W.W. Norton & Company, Inc., 2009), 653.

Though his goal as a politician is to save the Union, it is his election that is ultimately the final straw, causing the secession of the Confederate States. It is Lincoln's slow draw to the side of Abolition that makes the Confederate States believe that his election will be the end of slavery through the long feared "tyranny of the majority."

So what difference would Andrew Jackson being the 16th President instead of the 7th make? Very little, in my estimation. The slavery issue is easily the most dichotomous issue the United States had ever faced. As Thomas Jefferson once said of slavery: "But, as it is, we have the wolf by the ear, and we can neither hold him, nor safely let him go. Justice is in one scale, and self-preservation in the other" (https://www.monticello.org/site/jefferson/wolf-ear-quotation#footnote1_9uzfhab).

It is unlikely that Jackson's governing style would have done much to stifle the debate. Jackson appealed to the power of the majority, something which directly conflicted with the Southerner's debates in the 1840's, 50's, and 60's. From his First Annual Message to Congress in 1829: "...that the majority is is to govern..."

Despite the obvious fact that Jackson had passed away before the outbreak of the Civil War, it is unlikely that any one person could have prevented it. The political debates, which had been brewing since the Founding, and the events leading up to the 1860's election were finally coming to a head. The simple fact that the North could, through their majority, control who would become President, meant that secession was almost a certainty, and war soon after.

The bottom line is that the Civil War is the result of the South trying to hold on to the backbone of their booming economy, and the tradition of slavery, from being taken away by the majority in the North who finally wanted to do away with it. When someone says "The Civil War was about state's rights," they are not wrong. The question then becomes, "The state's right to do what?" Ultimately, it comes down to slavery.

There is a lot more to think about when it comes to the causes of the Civil War.. But from a political-historical perspective, I think the President's comments don't add up. Speculation on a hypothetical is not really something that can be done when it comes to history, regardless of how fun or interesting it may be.

I feel up to this point that no one has answered OP's question. People are just pointing out what the war was about. Why did it come to violence? Were all diplomatic methods exhausted? Were compromises negotiated? If so, what were they? Was there any mediation by other neutral parties (countries)? If so, who? Any last ditch attempts to stop the violence?

Link to interview?

If the Republicans decided to support slavery, and even pass an amendment guaranteeing the right to own slaves, would the South still have gone to war?

Georgia for instance stated they were convinced he Republicans were. It only anti slavery, but that being anti-slavery was the defining characteristic of the party. Could they have been convinced otherwise and if so, would war have been avoided?

I'm sort of curious if historians should delve into the question of morality on subjects of history -- Can slavery or the trail of tears really be considered objectively immoral by 19th century standards?

Was secession inherently 'wrong' if it was for the 'wrong' reasons?