The Final Straw: Lincoln's Election:1860

In 1860, there were two presidential elections in the United States. One took place in the North and one in the South. The South decided they did not like either the Republican or Democratic nominees and refused to allow them on their ballots. The split allowed Abraham Lincoln to win with 40% of the vote.
The Republicans believed they could win and needed a moderate candidate to allay fears they were extremists. They settled on Lincoln. Lincoln was a party organizer and moderate. He was also from a key state, Illinois.
The Democratic Convention was chaos. Stephen Douglas refused to allow provision in the party platform calling for Federal protection of slavery. He won the nomination, but the Southern delegates bolted and nominated Vice President John C. Breckinridge as the "National" Democratic candidate.
Meanwhile, the remnants of the Whig Party decided to form a "Constitutional Union" Party. This party wanted to keep the union together and disliked both the Democratic and Republican Parties. They nominated John Bell.
In the North, the election was between Lincoln and Douglas. In the South, it was Bell vs. Breckinridge. Since the Republicans were a Northern Party, the bulk of the population lived in the North, and the Democrats split, Lincoln captured the White House with just 40% of the vote. Shortly thereafter, South Carolina left the union. Lame Duck James Buchanan did nothing. Before he was even in office, Lincoln had a Civil War on his hands.