Answer:
The differences over slavery were at the core of the tensions that led to the Civil War.
In the South, the plantation economy was built on slavery. The southern elite believed slavery was a legitimate institution that they had a right to continue. They viewed the federal government as protecting their "property rights" in slaves.
The North moved away from slavery early on and developed more of an industrial economy. Most northerners came to view slavery as morally wrong and wanted it contained and eventually ended. They supported using the federal government to limit the expansion of slavery into new territories.
The Midwest was a mix of slave states like Missouri and free states. As more free states entered the Union, the political balance of power shifted against the South. This stoked fears of a federal government hostile to slavery.
The West was a key flashpoint as both sides wanted to control the expansion of slavery into new territories like Kansas, Utah and New Mexico. The struggle over whether these territories would enter the Union as free or slave states exacerbated tensions.
Together, these sectional differences over slavery's future in the U.S. - economically, morally and politically - built up over decades and eventually led to the Southern states seceding and forming the Confederacy, which in turn prompted the Civil War.
Hope this helps summarize how sectional disagreements over slavery contributed to the onset of the Civil War! Let me know if you have any other questions.