Take a look at a battle map. The north was clearly on the offensive while the south was clearly on the defensive--hence the name War of Northern Aggression.
You asked me to "prove" it wasn't about slavery. You've been on this forum a long time-- How much more evidence could one offer to you? If you can't understand that poor southern boys fought and died for their homes and families then nothing I say to you will ever convince you otherwise.
I'll try one last time though. In the museum at Shiloh, there are letters on display. One is from a southern boy describing his exchange with a yankee soldier. It was unaddressed at the time of his death so it was never sent. It basically says this:
Southern Boy: Why you tryin to kill me?
Northern boy: Free your slaves!
Southern Boy: I ain't got no slaves!
Northern boy: Why you tryin to kill me?
Southern boy: Cause you came down here to kill me!
Don't believe me? Take a trip to Shiloh, Tennessee and see for yourself. But that my knock down some of those blinders you wear, so I won't hold my breath.
Politicians exude a lot of BS, but it was poor uneducated boys who felt the need to stand up and defend their homes and property against northern soldiers who came as aggressors. There is always more than one causation to any war--quit broad brushing all southerners who fought in that war as a bunch of bigots. They weren't.
Those who illegally seceded from the Union were thugs and criminals, and got what they deserved.
The North wasn't after the South to free its slaves, it was after preserving the Union against outlaws who were dead in the wrong. The SOUTH seceded because slavery was threatened.
And before you go off on that blather about how most Southerners didn't have slaves (which in itself is untrue, since most of the time we think of the plantation owners as the slavers, when just about every family above the level of hardscrabble existence had at least one or two. It was what you did, just as in Latin America in our own day most middle-class families have servants) READ THIS detailed explanation written by a Southern newspaperman about why the "poor folks" of the South fought also to protect the institution of African slavery.