I have family members who believe the Civil war was about tariffs or "state's rights" while I was taught that slavery was the cause of the Civil war but I don't really have anything to proof it. So could I get some help from one of you with actual proof that the Civil War was about slavery?
As well as the FAQ answers already linked, /u/freedmenspatrol has a profile page with answers to questions on basically every part of civil war politics you might be interested in and the lead up. I particularly appreciate the answer on why the state's rights argument is completely fake.