How did the differences over slavery threaten the existence of the united states?

The north was opposed to slavery, and the south depended on slave labor. Therefore, the north and the south had opposing views on slavery. These views threatened to tear the U.S. apart, because some southern states threatened to secede from the Union, and the south was angry that many slaves escaped by running away to the north. Plus, the north ridiculed the south for ever allowing slavery, after northerners read the controversial novel, Uncle Tom's Cabin. It seems that neither side could think of a compromise. Eventually, this resulted in the Civil War.