This was probably the result of a misguided compromise, since folks couldn't agree on what to call it, "The Civil War" or "The War of Northern Aggression".
It's a shame, because while I think that slavery was reprehensible, the South has also much to be proud about as well. Many brave, honorable (and highly skilled) men fought for the South. For the most part they didn't see themselves as fighting FOR slavery, but rather FOR states rights. In the end, they, and their Northern brethren, were betrayed by fire-eating politicians, who proved to make terrible generals.
This spin may seem pretty amazing to those of us who grew up in the liberal Northeast, but the sad fact is that it's the standard story among many Americans, particularly in the South. The soldiers were usually fighting honorably --- no, nobly --- for states' rights. Slavery? Merely incidental. In this version of events, the Civil War was like a tragic argument between two parties that were roughly equally wrong, rather than a case of the South's fighting tooth and nail to perpetuate a monstrous violation of human rights.
Downthread, Roger corrects Jay's version of events:
... I've read some recent (excellent) work that has looked at the events leading to the War. What they've found is that there is hardly a single speech given by ANY leading (or even minor) successionists prior to 1861 that wasn't almost entirely focused on the preservation of slavery. And there were a LOT of speeches; successionists had fanned out across the south, and were furiously trying to rouse the masses to their cause. They gave hundreds if not thousands of stump speeches, and transcripts, news reports, and original texts confirm that slavery was always THE issue. "States Rights" was simply not a major rallying cry, except in the context of the preservation of slavery.
So when did "States Rights" as a separate idea appear? Almost the day after the war ended. Southern Revisionism began quickly, and was flogged by most of the leading Southerners who'd previously led the Confederacy. But at least for the duration of the war, most Confederates were quite explicitly fighting for slavery, NOT for "States Rights."
The work Roger's referring to is probably Williams College historian Charles B. Dew's recent work Apostles of Disunion (bookstore links). The U. of Virginia Press's abstract for the book has this to say:
In late 1860 and early 1861, state-appointed commissioners traveled the length and breadth of the slave South carrying a fervent message in pursuit of a clear goal: to persuade the political leadership and the citizenry of the uncommitted slave states to join in the effort to destroy the Union and forge a new Southern nation.
Directly refuting the neo-Confederate contention that slavery was neither the reason for secession nor the catalyst for the resulting onset of hostilities in 1861, Charles B. Dew finds in the commissioners' brutally candid rhetoric a stark white supremacist ideology that proves the contrary. The commissioners included in their speeches a constitutional justification for secession, to be sure, and they pointed to a number of political "outrages" committed by the North in the decades prior to Lincoln's election. But the core of their argument--the reason the right of secession had to be invoked and invoked immediately--did not turn on matters of constitutional interpretation or political principle. Over and over again, the commissioners returned to the same point: that Lincoln's election signaled an unequivocal commitment on the part of the North to destroy slavery and that emancipation would plunge the South into a racial nightmare.
Before the war, President Buchanan had rejected Kansas's petition to abolish slavery, and the Supreme Court's Dred Scott decision mandated governmental support of slavery even in states which had determined to reject this "peculiar institution." Both of these decisions were clear violations of the doctrine of states' rights, yet slaveowning Southerners cheered. The problems came with the possibility that future states, given a free choice (and a Republican presidency), would not embrace slavery -- and might even endorse social and political equality for Black Americans.
By the way, do read the other Amazon reviews, where a bunch of adherents of the Civil War revisionist school nitpick or propose ridiculous counterfactuals whereby the North would have been the ones fighting for slavery. Yes, fine, that's all well and good, but the fact is that in this universe, the thing that got Southern soldiers to line up for duty, to kill or be killed, was the fear that the niggers would become free.
Now, I frequently read arguments that "Well, the North was fighting mostly for economic reasons, so the South couldn't have been fighting to preserve slavery." This argument is disingenuous: it ignores the simple fact that combatants need not be fighting for the same reason. The fact that the South was fighting to preserve slavery does not require that the North be fighting to end slavery.
In fact, the standard narrative I was taught is that the North wanted to preserve the Union, whereas the South wanted to preserve slavery. Louis Menand's superb book The Metaphysical Club (bookstore links) touches on this in some detail: before the Civil War became imminent, most Americans viewed abolitionism and Union as diametrically opposed. In order to preserve the Union, the abolitionists had to shut up, because they were pissing off Southerners. It was only much later that the causes of abolition and Union became conjoined; and it was the Southerners' (probably mistaken) belief that the Lincoln wasn't going to preserve slavery that joined them.
Anyway, all this is just to say: if you ever see someone, online or off, going on about how the South was was fighting for the noble cause of states' rights, then point them to Dew's book. Or just ignore them. They're full of it.