I will partially agree with Telahnay on his post, but Lincoln's decision to make the eradication of the "peculiar institution" a war goal did not come until the summer of 1862. Lincoln's initial callup of troops was to restore the Union. I, too, was a history major in college, and have an ancestor that died at Chickamauga for the Confederacy.
My opinion for the cause of the war lies in the rights of states and property owners. The northern states, who also had an institution of slavery until mid-18th century, and many of their citizens and elected representatives in Congress, attempted to dictate policy and property rights to southern propertyowners. Cases in point include abolitionist tracts circulated in the south to incite slave revolts, the underground railroad, and the various safety committees that sheltered fugitive slaves. Many northern states protected their citizens who sheltered fugitive slaves, in direct contravention to Federal law, which deprived southern citizens of their property rights. This went on all through the 1850s.
I could go on with more examples, but I think I have said enough to illustrate my point. I think the war erupted as a result of one group of society trying to usurp the rights of another. Certainly, there were firebrands that took efforts to make the war happen, such as Edmund Ruffin and William Seward. There will always be people behind the scenes pulling strings.
I conclude by again saying that was the war was in defense of rights granted, guaranteed and secured by the Constitution. The South rose up in defense of her rights when elements of Northern society denied and usurped those rights. I cannot speak for other people on this forum, but I know I would fight if someone was in possession of my property and not return it, which is theft of property as I understand it. The challenge for us today is to come together as Americans, even though the legacy of the agitators is a sustained campaign to eradicate the Southern heritage. Like the private said in the movie Gettysburg said, "Live and let live I heard some folks say. Seems like there would be a lot less fuss and bother if more people took it to heart."
Jim