Debate the Civil War and what it means, and inevitably you'll get back to the purpose of the Confederacy and why it existed in the first place. Was it a race/slavery thing? Or was it more complicated and involved a lot of overlapping factors? I have some friends who lean strongly to the latter; that while race/slavery played a role, it was just one of many factors and it's not right to single it out from others.
I disagree strongly.
I'm happy to concede that there were multiple overlapping factors leading up to Southern Secession and the eventual formation of the Confederate States. But I can't understand how anyone looks at history and doesn't come away understanding that slavery, specifically race-based slavery, was unique and was the central driving force behind everything. "States' Rights" comes up often. But States' Rights wasn't some academic debate that got particularly heated. It was States Rights for the sake of X ... and X was the continued treatment of black people as property. Put another way, "States Rights" was the argument, the means to the end. The end goal was race-based slavery.
We don't have to guess at this. All we have to do is look at what they said at the time about why they were doing it. Some of them (see below) even explicitly rejected the notion that the Civil War was "States' Rights" over slavery, calling it a "new fangled heresy" conjured by diplomats to make countries like France and Britain more open to helping the South out.
Just take a look and decide for yourself why they were doing this:
Alexander Stephens, Vice-President of the Confederacy, "Cornerstone Speech"
Our new government is founded upon exactly [this] idea; its foundations are laid, its corner- stone rests upon the great truth, that the negro is not equal to the white man; that slavery -- subordination to the superior race -- is his natural and normal condition. This, our new government, is the first, in the history of the world, based upon this great physical, philosophical, and moral truth.
Richmond's "Southern Punch" Newspaper, 1864 (emphasis in the original):
"The people of the South," says a contemporary, "are not fighting for slavery, but for independence." Let us look into this matter. It is an easy task, we think, to show up this new fangled heresy --- a heresy calculated to do us no good, for it cannot deceive foreign statesmen nor peoples, nor mislead any one here nor in Yankeeland ... Our doctrine is this: WE ARE FIGHTING FOR INDEPENDENCE THAT OUR GREAT AND NECESSARY DOMESTIC INSTITUTION OF SLAVERY SHALL BE PRESERVED, and for the preservation of other institutions of which slavery is the ground work.
Virginia's Secession Ordinance:
The people of Virginia, in their ratification of the Constitution of the United States of America, adopted by them in Convention on [June 25 1788] having declared that the powers granted under the said Constitution were derived from the people of the United States, and might be resumed whensoever the same should be perverted to their injury and oppression; and the Federal Government, having perverted said powers, .
Mississippi's Declaration of Cause:
Our position is thoroughly identified with the institution of slavery-- the greatest material interest of the world.
South Carolina's Declaration of Cause:
[A]n increasing hostility on the part of the non-slaveholding States to the institution of slavery, has led to a disregard of their obligations, ... the current of anti-slavery feeling has led her more recently to enact laws ... they have denounced as sinful the institution of slavery ... because [Lincoln] has declared that that "Government cannot endure permanently half slave, half free," and that the public mind must rest in the belief that slavery is in the course of ultimate extinction.
Georgia's Resolution to Dissolve:
For the last ten years we have had numerous and serious causes of complaint against our non-slave-holding confederate States with reference to the subject of African slavery ... [a] brief history of the rise, progress, and policy of anti-slavery and the political organization into whose hands the administration of the Federal Government has been committed will fully justify the pronounced verdict of the people of Georgia.
Texas' Declaration of Cause:
[Texas] was received as a commonwealth holding, maintaining and protecting the institution known as negro slavery-- the servitude of the African to the white race within her limits ... We hold as undeniable truths that the governments of the various States, and of the confederacy itself, were established exclusively by the white race, for themselves and their posterity; that the African race had no agency in their establishment; that they were rightfully held and regarded as an inferior and dependent race, and in that condition only could their existence in this country be rendered beneficial or tolerable.