The conflict between regions that finally became the civil war began to "come to a head" during the

Election of 1860

Explanation:

The Election of 1860 was the pivotal presidential election because Abraham Lincoln ran against Stephen Douglas and the main discussion of the election was slavery and state’s rights.

Also during this election, the Democratic Party split over the discussion over slavery. Because of that Southern Democrats nominated John Breckinridge that was a supporter of slavery at the same time Stephen Douglas was running for the Northern Democrats.

Even though Lincoln won the election, the crisis was already installed between North and South and before Lincoln’s inauguration 11 Southern States had already seceded from the Union.