The main reason that the Civil War erupted in the United States in 1861 was the conflict between the North and the South on the issue of slavery. For the Southerners the debate about slavery gradually evolved into an economic issue based on money and power. The South's economic system was based on cotton, which needed slaves to work the fields. .
In the North, some disliked slavery because they felt it was wrong. Most people did not have an opinion on the matter, and even some people condoned it, because abolishing it would be bad for business. They thought that without the slaves, there would be no cotton. Without the cotton the textile industry would suffer. .
It all started with the Missouri Compromise of 1820, which was enacted by Congress to put limits on the spread of slavery in what was left of the Louisiana Purchase. The Compromise admitted Maine as a free state and Missouri as a slave state in order to keep a balance between the slave states and free states. The South had an economic interest in the spread of slavery to the new territories so that new slave states could be created and the South's political influence would remain strong. The North had an interest in limiting the spread of slavery into new territories for both purposes of controlling Southern political power and supporting the moral issue. .
In 1854, the Kansas-Nebraska Act made slavery possible in any new territory. Senator Steven Douglas supported this Act and wrote in popular sovereignty into the bill, which left the issue of slavery up to the people who lived in the territories and their appointed representatives. People in the North became aware of the danger of the potential spread of slavery. .
The fate of the Union rested on the election of 1860. The newly formed Republican Party nominee was Abraham Lincoln. The Democratic Party was split between the loyalist and those with slave-holding interests. This Democratic split was the cause of the eventual downfall of slavery by Lincoln.