What do you feel the most important election of US history is?

[Unconditional Surrender Truman]

1860 is objectively the correct answer. No other electoral contest has so fully and irrevocably decided the national character.

[Unconditional Surrender Truman]

1860 is objectively the correct answer. No other electoral contest has so fully and irrevocably decided the national character.

No that's 1800. 1860 had the most important nominating convention as who the Republicans chose would have a major impact, but the South acting like spoiled brats was inevitable that year.

Is not that nominating convention a part of the election? It's beyond dispute that the South was going to try and break off from the Union in 1861 no matter what. Far less certain was the Northern response to secession. A stronger showing by Douglas in the Old Northwest might well have been enough to elect Democratic state governments in Illinois and Indiana — two states whose unequivocal support for the Union during the war was decisive in the fighting on the western front. Replacing Oliver Morton with Thomas Hendricks as governor of Indiana from 1861 to 1865 absolutely changes the course, if not the outcome, of the war (Lincoln himself considered Morton so important to the Union war effort that he personally appealed to General Sherman to furlough his Indiana soldiers in time for them to return home and vote for Morton's reelection). Instead, the Northwest closed ranks with the upper North to support the Republican ticket in 1860 — a result that was anything but inevitable and everything but inconsequential.

[Unconditional Surrender Truman]

1860 is objectively the correct answer. No other electoral contest has so fully and irrevocably decided the national character.

No that's 1800. 1860 had the most important nominating convention as who the Republicans chose would have a major impact, but the South acting like spoiled brats was inevitable that year.

Is not that nominating convention a part of the election? It's beyond dispute that the South was going to try and break off from the Union in 1861 no matter what.

That assumes that the Republicans win the White House in 1860.  Assume for the moment that Democrats either hadn't had their 2/3 rule or Douglas manages to get nominated in Charleston despite it. The result is a Douglas victory:
[snip]

That's the issue, though: Douglas could not keep the support of Southern Democrats without giving up the Freeport Doctrine wholesale, and he could not do that without loosing the support of his Northern base. Bear in mind that, to win or even deadlock the electoral college, Douglas would have needed to improve on his actual performance in Illinois and Indiana; I don't see how he could do that while simultaneously winning over the Breckinridge camp. The two-thirds rule was not what split the Democratic Party; it was the insistence of Southern Democrats on nothing less than total commitment to the unfettered expansion of slavery into the territories. That ticket simply could not carry Illinois or Indiana in 1860 (or even 1856), and popular sovereignty was no longer acceptable to the Davises and Breckinridges of the party. Douglas made his choice in 1858 when he sired the Freeport Doctrine as the antidote to Dred Scott, and as a result was nearly as unpalatable to the Southern states as Lincoln was.

The only quasi-realistic chance of preventing civil war in 1860 was to throw the election to the House and somehow elect Bell as a compromise candidate; but the math and the passions of the times combine to make that scenario, at best, a long shot.

EDIT: Come to think of it, this would make an interesting alt-history timeline on the What If board.

[Unconditional Surrender Truman]

1864. Had Lincoln not won reelection, McClellan would have allowed the South to secede from the Union in order to end the war sooner. The United States would have been split in two countries, if not more since a seccession precedent was set.

McClellan himself was never actually in favor of a negotiated peace, and explicitly repudiated the peace plank in his original letter accepting the Democratic nomination. Considering Lee's surrender came a little more than a month after the inauguration, I rather doubt a McClellan victory dramatically changes that outcome; on the other hand, the prospect of Lincoln's impending retirement likely removes the incentive for outgoing Democratic congressmen to vote for the 13th Amendment in January 1865, which certainly changes the legacy of the war.