RE: Civil War - it was about slavery and it wasn't. It was more about losing the poor white laborers to the old west, and not being able to claim the land for themselves [which is to say the 1800s version of the 1% didn't want to share with anyone else; but how do you say 'We're seceding and fighting with the north because we want to keep the majority of you down under our heel? Because how many poor laborers are going to fight if that's the case.
I half suspect that the whole 'I'm not poor, I'm just a millionaire down on my luck mentality was fostered then, except it was 'Well, one day I'll be rich enough to own slaves too' and so being told 'We're fighting to keep our time honoured institution of slavery' was seen as something worth fighting for, even if you were logically never going to be rich enough to own slaves yourself.
Also, at least one northern in history that I know of became a seceding slave owner - the Mass. gentleman who came to Pensacola to build Fort Pickens; ironically, it was that fort that managed to reclaim the city for the Union.... yeah, I'm a history buff too, and that bit cracked me up.
Anyway, like most things, though, its a bit more complicated. Just like the Union did not -just- fight to free slaves. The south was the agricultural center of the country, and the north was industrial. But it sure does sound grander to say 'We're fighting to free the slaves and preserve the Union'.
And it was of course that, too, though the best reason would be 'They started it." [The Confederacy -did- in fact start it, and not by leaving]