Answer:
For decades before the Civil War, there had been several attempts at resolving the hostilities between the Free North and the Slave South such as the Missouri Compromise.
The North then increasingly became Republican which was a party that championed the abolition of slavery not just the limiting of it and this led to further confrontation with the South.
These issues came to a head on May 22, 1856 when Congressman Preston Brooks from South Carolina brutally caned Senator Charles Sumner in the US Senate for Sumner's anti-slavery rhetoric.
This proved that tensions had ran so high from the issue that it had passed beyond being resolved by reasonable discourse because it showed that both sides were so staunch in their beliefs that they would not concede anymore in their demands.
All that remained therefore was to enforce the beliefs of one on the other and this could not be done by negotiation, only through violence.
