Union for me.
I remember in my History class my teacher was talking about how the war was about slavery.
I asked him about state's rights as a possible reason. His response was "A state's right to what?"
He was born and raised in Georgia and one of his ancestors was in the 33rd Virginia.
In so which, even though I hold no animosity towards any southern inhabitant of these Untied States, the war was about slavery. The only reason the south despised Lincoln was because he was an abolitionist. Any other explanation can be linked back to the source cause, slavery.
God bless the US.