Lincoln’s victory in 1860 was largely due to a split in the Democratic Party, which ran separate candidates in the North and South. Secession and the Civil War followed shortly thereafter.
When you look at this objectively, there really wasn’t a good reason for secession; the likelihood of legislation prohibiting slavery in the territories getting through Congress was pretty slim even with Lincoln’s support. I think it is fair to say that the war was the result of weariness in dealing with the slavery issue and terminal impatience; it was not, at least at that point, inevitable.
The outcome of the war enshrined the principle that the USA is a perpetual compact made by all of its people, not a marriage of convenience among individual states. That principle has contemporary relevance, too; in the event of a Clinton victory, you can expect some new secession talk as well as sporadic violence in red areas of the country.