Sure, there's no doubt that slavery was a large issue. A point that some have mentioned: If slavery was "the cause", all the North had to do was buy the slaves and set them free. The cost, based on the slave population and the value per slave, would have been much less than the actual cost of the war in dollar terms, and I think it's obvious that there would have been far fewer dead bodies. But, as we all know, ego usually wins out over reality...
Ask yourself why the 95% of non-slave-owners would suport the Confederate views? Why would they be willing to enter into a war on behalf of an upper economic class?
That's essentially been an unasked question, seems to me. It's when you look into the taxing structure of the country and the ancient "Cui bono"? that you start to see a larger picture. Add to this an attitude of "Who are they to tell us how to live?" and you might better understand the views of the lower economic strata of the South who were the foot-soldiers.
Another factor, seems to me, is that if you enter into a political union that turns out not to be of benefit to you, why must you be forced to stay? This was not like a contract for repaying a loan, which is indeed an obligation. It was a joining together of individual states into a union, and it began to be detrimental to the agrarian states because of tariffs (making earning a living more difficult) and the national tax structure.
Even "Civil War" is a misnomer. The South did not want to conquer and control the North. Civil Wars have always involved a fight between two groups for control of an entire country. The Confederates merely wanted to leave the Union.
A question for today: If a large majority of the citizens of any U.S. state--or states--desire to no longer be part of the U.S., what's wrong with their seceding? What's morally wrong with that? I'm not talking about "Is it legal?" What reasons justify forcing people to remain as part of a political union which has become anathema to them? I can't accept some variant of, "We want your tax money, so that means you can't secede." That's not in line with the meaning of liberty, of freedom.
If you're having a party at your house and some get perturbed at insults from others at the party, do you tell the upset folks that they can't go home?
Art