According to Loewen, 50% of Americans don't think that slavery was the real issue (25% for States rights, 12.5% for Economic issues, and 12.5% for Taxes and Tariffs). Even the state of South Carolina has a monument at Fort Sumter claiming states rights as the issue. The reason states rights keeps coming up was that the South was upset at all the free states not enforcing the slave articles in the Constitution. That's what caused the passing of the Fugitive Slave Act (basically provided monetary incentives to judges to enslave all black people brought to court, free or not) and the result of the Dred Scott Supreme Court decision.
Abraham Lincoln was most likely elected because the Northern and Southern Democrats split as a result of Stephen Douglas's (Democratic candidate for president) favoring the State's right to decide whether it was free or slave, instead of following the Missouri Compromise calling all states south of Missouri (including Missouri) slave states; the South wasn't very happy with this.
And as far as Economic Issues and Taxes or Tariffs, those are the minority of people and I don't think much needs to be contended there.
I thought that it was rather obvious that Slavery was the issue.
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Update:
A few evidences that States Rights is not the true issue:
- "Shortly before the war, in 1861, Jefferson Davis defended secession as an act of self-defense against the incoming Lincoln administration, whose policies of excluding slavery from the territories would 'make property in slaves so insecure as to be comparatively worthless, thereby annihilating, in effect, property worth thousands of millions of dollars.'
- "Well after the war, in 1881, Davis changes tack and says, "The South fought solely for the inalienable right of a people to change their government, to withdraw from a Union into which they had entered and into which they had as sovereign communities voluntarily entered. The existence of African servitude was in no ways the cause of the conflict but only an incident.'"
The other two ways are that it renamed the war to "The War Between the States" (which lasted from 1890 to 1970) and that they won it on the ground ("In county after county, even in the North, Confederate monuments sprang up." For example in Kentucky, a state that did not secede, you'll find 74 Civil war monuments, 72 of which honor the Confederacy! "The effect of a Confederate landscape makes it easier to have a Confederate mind and heart.)