Well this is new, apparently the American Civil War was actually the American War of Independence Part II right down to the causes thats a load of bullshit.
The main reason was actually the slaver states fearing loosing control since they would be eventually be outnumbered and the strengthen of Federal powers and Presidential powers, this was simply a case of they had the bizarre idea the US was the UN were they would just leave, the US didnt take kindly over trying to take over FEDERAL installations that was the major Confederate mistake.
Of course Southerns tell a different story, like all LOSERS do (except the Japanese that pretend it never happened) ... but it was just a question of state rights over the increasing centralization of power because in order for the US to function AS A NATION it could not be second guessed by shitholes like Texas because of the whole association of States, it had to centralize power and it could only be at the expense of the states own Independence, Slavery was just the crux of many issues in relation to Federal legislation and created 2 distinct camps.
If Slavery was that important why the fuck did the Confederacy allow it to be abolished it 1864? In fact their stubborn refusal was a major cause of not having any foreign allies since the rest of the world was moving to abolish it, attempting to hold to it because of a moronic sense of racial superiority would have completely sunk the Southern economy when Industrialization come at full swing, we did not as much free slaves as we get something better to replace them.
First off the roots of the war go back to war of independence. The south did not really even want independence in the first place. They liked things as they were, an agrarian plantation society. It was the north that wanted independence and that wanted to become a trading and industrial powerhouse. The north hadn't the right climate for the good cash crops like the south, and the south hadn't the resources for industry like in the north.
North did most of the fighting in the war of independence, and pushed for it. Many southern loyalists and some from new england actually left the country to go to cucknada after the war, they were so choked about the outcome.
After the war there was this gigantic war debt, and the south FROM THE START tried to get out of it and absolutely resisted any form of federal government. They wanted each state to have absolute self determination - a republic. Their interests were nothing like the interests of the north. Only because Alexander Hamilton worked very hard to convince them to come on board did they agree to allow any federal taxes AT ALL.
So of course since the south was outnumbered and the whole point of the war was a northern thing and they ALREADY hated the south, the tariff situation was completely reversed. Instead of taxes that put a hardship on mercantile and industrial concerns the taxes were shifted to agricultural exports, and not as anything to do with slaves. They did it because they wanted to become an industrial power and stop being a supplier of raw goods to europe, because in that way they can make much more money. Effectively speaking, if the south wanted to sell anything they had to sell it to the north instead of europe!
The FIRST THING THEY DID once a federal army was established was to set up forts in the south full of soldiers to make sure no one could smuggle any goods out of the ports without paying export excise taxes (which is now unconstitutional, because export tariffs are completely fucking retarded!).
On top of that, the south was forced to stomach a much larger portion of the war debt per capita this way. Again this is punishment for not going along with the war of independence fully in the first place, not to mention staunchly resisting formation of a federal government.
Leading up to the war, Lincoln even promised that there would be a pro-slavery ammendment so long as the south would remain in the union. They didn't even pause to consider the possibility. Lincoln also believed all africans should be sent back to africa, something that is not pimped out by the media very often.
So no, slavery was nothing to do with anything.
It wasn't until hollywood started rewriting history did this idea even occur to anyone.
Edit: the only way that slavery entered into it was to keep the french from entering the war, which is why the slaves were freed - the french wanted to enter the war and make a combined mexico-southern US empire, but they did not want to be seen as supporting slavery over freedom.
This whole thing was another reason for the war and why the south was being punished. The north worked hard to keep france out of north america, and things could easily have gone in a very different direction.