Answer:
Slavery, Lincoln Election.
Explanation:
The main issue of the Civil War was slavery. Slavery was considered an abhorrent practice by most of the people in the North, where it was illegal, and many people in the South, where it was legal, but, because the Southern Economy was based on slave labor, the election of Abraham Lincoln came to represent a threat to the Southern Economic System.
Several attempts like the Missouri compromise had been made before the war, in order to reach a agreement between the pro-slavery states of the South, and the anti-slave states of the North. However, this compromises did not achieve their goal, and there were many tensions.
Lincoln, and his republican party, represented the idea of abolishing slavery, at least in the new territories of the United States, because Lincoln never really said that he wanted to end slavery in the South. However, after his victory, the Southern states felt that slavery was threatened, and decided to secede, which started the war.
At the end, the North won the war: it was wealthier, had more industry, and more military. Lincoln was also a more effective leader than its southern counterparts. The Southern states were right in the sense that the Norther victory represented the end of slavery in the United States.
