Why did southern states leave the union

Lincoln was nominated by the republican party, which had taken a public position against the expansion of slavery into the newly acquired territories. furthermore, his personal views against slavery were well-known, and he was perceived as a strongly partisan, anti-southern, abolitionist candidate the union and the confederation did not agree on some points, and it lead to a separation between the two. confederates were for slavery, union members were not. but even then. not all slaves were treated equally even when free.