@Rolan:That's pretty much flat-out wrong, the Civil War was entirely slavery-motivated.
States' rights was the modern justification.
It's really not that simple, though. I could say "It was about the states' rights to run their economy and citizenship", but even that would be simplifying it.
As I learned it, the southern states were in the wrong on slavery. And that slavery allowed them to harvest large quantities of raw materials, which they could ship to the northern industrial states or to industrial nations like Britain - except that faced harsh tariffs if they tried to ship overseas. They were forced to deal with the northern states, which took full advantage of the profitable situation.
At the same time, the northern states (who had less, though certainly not *no* use of slaves) started getting preachy and demanding that the southern states emancipate. This was a devastating idea, and one not supported by the southern voters (particularly when they got extra votes from their owned slaves). "No, we'll manage our own business thank you very much."
This lead to an *inevitable* conflict, which Lincoln inherited and tried to continue to delay. But despite his efforts to maintain the status quo, things came to a head.
Long story short: The USA pressed a claim on the southern states that I don't recognize. And won. But here's where things get way better than expected. Not only did the northern states abolish slavery, they were also magnanimous in victory. They helped the southern states rebuild our economy not to rely on slavery (technically. Tenant farmers and wage-slaves are a bit better though). The secessionist politicians, instead of being executed as traitors, were allowed to rejoin the USA and had fairly mediocre political careers.
The USA unjustly forced the southern states to become more progressive and it actually worked. Because they used a soft hand, and because the common folk of the South weren't that attached to slavery anyway (the institution mainly benefited the rich). It all worked out well, even if the casus belli was crap.
Sherman should rot in hell for what he did. Lee should go down in history for refusing to lead a bloody guerilla campaign.
Lincoln was not some shining paladin, he was a politician who kept his country in one piece.