Basically the southern states wanted slavery and the north didnt allow it ( first situation) then sectionalism happened between the north and south when new states like cali wanted to be a free state, distrupting the balance of free and slave states (second situation) and also south favored states rights and north wanted unity (third situation. ) and basicaly the south has had enough bs and left the union to be the confederacy. thus the civil war started. also when Lincoln won 1860, the southerners saw this as a threat to their state rights and slavery (fourth situation) thus more sectional tension :))) isn't the civil war great:)
