What kicked off the war was not slavery -- that had been an issue for a long time before the war.

Right before the war started, a few events happened in succession. These events gave the South the confidence that was required that secession was a good idea and war an even better idea. These events were:

1. A market crash that wiped out vast fortunes of Northern money. The events leading up to this crash were that it became clear the West would be just as divided as the East, except this time everyone had a gun and was willing to use it. The idea of laying railroad tracks to bring back cheap and plentiful economic products had disappeared. It was likely the West wouldn't be making anything worthwhile except war.
2. Cotton was rising in prices, and had been a staple of income for the South for generations. The phrase "King Cotton" meant that cotton was a superior market to be a supplier in, much better than factories and machinery. After all, people needed cotton clothing; they did not need steam engines.
3. Tariffs on the machinery needed to make cotton meant that the South had to buy their machines at a markup from the North.

In effect, it appeared to the South that the North was milking their economic product and taking advantage of the one industry that was keeping America afloat. If the South cut ties with the North, then they could make even more money and at the same time the North would be totally bankrupt and have to go back to agriculture and subsistence farming.

You must understand that even though the United States were a vast economic engine that dwarfed any other country, and probably exceeded all of Europe at the time, Americans still felt like they were small players, relatively weak, and at the mercy of Europe. It wasn't so long ago that the Monroe Doctrine was introduced, and it was not at all clear that the United States would ever be able to enforce it. Indeed, by the time the Mexican-American War rolled around, pretty much everyone was betting against America. They were pretty sure that Mexico's superior culture and military would totally annihilate America's hodge-podge of second-rate commanders and volunteer militia.

What confounded matters was that the North elected Abraham Lincoln, the one guy who the South said they were violently opposed to. Lincoln's election meant that the South would no longer dominate the presidency, and that meant that the Supreme Court would, over time, shift from the South to the North. It was a matter of political expediency to sever ties before the court shifted to the North. However, I do not think this was really a pressing issue. The effects of Lincoln's presidency, if any, would take decades to manifest. I think it only made clear the North's intentions to the South, and exacerbated the economic issues.

The reason for the violence from the South is hard to tell. Some of it was in the spirit of reparations -- we'll take your guns and ammo and food as payment for the money you stole from us. Some of it was just plain looting. And some of it was probably irrational exuberance -- "We got em on the run, why stop now?" Maybe the Southern spirit of competition had a part in it too. "Oh, Mississippi did that? We can do TWICE as much!"

Was slavery an issue behind all this? Absolutely. But slavery was the constant. The variables above explain why the Civil War happened at this time and not earlier. Those things above were the straws that broke the camel's back, but pale in comparison to the mighty weight of slavery that affected everything.