My GGGF was a slave owner and a corporal in the US Cavalry. Sure, he was fighting for slavery.
I believe that too. I had a GGG uncle who set his slaves free and gave them a generous amount of land years before the war when he volunteered in the rebel army. But that has very little to do with the secessionists, a whole different group, seceding over slavery.
Four out of Five of my confederate ancestor soldiers did not own slaves. What were they fighting for?. I guess an opressive invasion might had something to do with it.