The US Civil War — like World War I† — was a conflict that was almost destined to happen based on the escalation of relations amongst the states and between the states and the federal government. Like the First World War, we can identify “who fired the first shot” and that was South Carolina. This happened because the Southern states were increasingly afraid of the anti-slavery movement in the North. This movement reached a feavered pitch to the point where Northern states were openly assisting escaped slaves. Furthermore, Lincoln repeatedly railed against slavery. He never came out and said, “I will end slavery” (he wasn’t that bold), but his anti-slavery stance was part of his campaign.
The South, not wanting to deal with Northern encroachment to what they considered a “states rights issue” (the right of certain states to permit slavery), inevitably saw this as a threat to their way of life, their economics (agriculture depended on slavery at that time) and thus their prosperity. They saw that the North was increasingly more populated and more industrialized and could no longer suffer the indignity of being out-voted by that block. With Lincoln as the last straw, they banded together to declare their independence. When Lincoln would not acquiesce, the state of South Carolina fired Ft. Sumpter.
†The US Civil War was a direct precursor to the First World War as a transitional war. The Europeans actually had observers in the US Civil War to inform them how to fight their next war. So, even if US history bores you, the Civil War is an important conflict in how it directly affected the First World War.