If it wasn't about slavery, what was it about? It seems to me it was about the fear of slavery being limited only to the existing slavery states and not in the newly acquired territory gained from the Mex-American war. That, and the worry that transporting a slave across a free state could potentially cause that slave to be free, or in other words, a loss of personal "property" that the southern states felt was unconstitutional. I know a lot of people have tried to say it was "states rights" but I'm not sure what states rights were being violated or could have the potential to be violated? At no point did the North demand an end to slavery, those calls only came from the extreme elements and not the mainstream political elements.
There were many northerners who did not sympathize with the abolitionist movement. Harriet Beecher Stowe wrote a simple, little book that had a major impact on the gaining of momentum of the abolitionist movement. The book is entitled, "Uncle Tom's Cabin." Northerners started to read it and it shifted attitudes. It put pressure on the government to do something about the institution of slavery.
Let's keep in mind that the wealthy, southern aristocracy was a minute number of men. The average southern, white was poor, and were being exploited by the aristocracy. There wasn't much opportunity for upward mobility, for poor whites. They were given trivial jobs and treated as an underclass. In movies, their often depicted as overseers. Some of them managed to eventually earn enough to buy property and own a few slaves, but most didn't.
What I find interesting , is that rich, southern whites and politicians, concocted the notion of upward mobility for poor whites, and they convinced poor whites to buy into the war being about northern aggression and a violation of state rights. Why? Because they needed soldiers to fight. As far as what the true name of this war was, it's a matter of perspective. Southerners called it "Northern Aggression." Slaves called it the "Freedom War," while many northerners called it the "War of Secession." Everyone had their own name for it, but the bottom line is that it fits the dictionary definition of a civil war, and that's why the majority of Americans call it, "The Civil War."
Also, let's keep in mind that the south fired on Fort Sumter, which was a US Army installation. The south claimed that they had a right, due to their secession from the Union and that the supply ship that Lincoln sent into Charleston Harbor was an act of aggression. The war was started by the south. The Union justified it, by using the idea that no state has a right to secede from the United States and that they had a right to occupy any military base within the nation.