The root causes are much more diverse, but I believe that nearly every cause can somehow be linked back to slavery and land -- the South's dependence on expansion of those two resources, and their realization of the trap they had set for themselves with the Compromise of 1850, put them in desperate realization that they were ultimately facing checkmate.
Once the North had gained the majority in the Senate, and with the ensuing melee over Kansas statehood, the South realized that expanding slavery into new territories would not happen. At that point, the only thing that would have prevented the Civil War would have been the tractor.
While Southerners offered various reasons for supporting slavery, ranging from the guiltily paternalistic to the hideous "justification" that Africans were created to be the slaves of Europeans (there were indeed Southern ministers who preached the "two creations" theory), deep down inside it was that the slave was simply the fuel for a slave economy.
I once heard a lecturer in New Orleans make a great comparison: it would be as if the government had suddenly said that farmers could not use deisel fuel and therefore could not run their farm equipment, and offered them no compensation for the fact that they would immediately no longer be able to operate their farms and in fact that their regional entire economy would collapse overnight. The economy of the major slave states was entirely a slave economy, and regardless of what theoretical justifications they gave, it was basically that the slave labor of these millions of Africans was the fuel for their economy.
So perhaps the invention of the tractor would have solved the problems. A slave economy is the least efficient of all, and in fact one of the reasons slavery collapsed in Europe after the fall of Rome (initially being replaced by feudalism) was simply that it was cumbersome and costly, both in terms of the ultimate cost of the labor and in terms of the need for security when you had to force millions of slaves to keep laboring to support a tiny handful of masters.