Why was the election of Lincoln the catalyst for the Civil War?

In his 1860 campaign for the presidency, Lincoln pledged to oppose the extension of slavery. Although Lincoln heartily detested the institution, he wasn't planning to abolish it outright as he knew it would be politically impossible. Besides, for Lincoln the most pressing priority was keeping the Union together through a particularly stormy period in its history. If that meant retaining slavery, so be it.
But Lincoln's nuanced position on slavery was lost on Southern opinion. Right from the outset, it perceived Lincoln as a serious threat to a whole way of life. The vast majority of Southerners genuinely believed that, sooner or later, Lincoln would abolish slavery altogether, irrespective of what he'd said on the campaign trail.
When the results were counted, Lincoln failed to carry a single state south of the Mason-Dixon line; he wasn't even on the ballot in most Southern states. But he'd won the election, and that was the main thing. As soon as Lincoln's victory was confirmed, the Southern states began making preparations to secede from the Union. South Carolina was the first to go, formally seceding just over a month after Lincoln won the election.