Therefore the war could not be about something that wouldn't change. It had to be about something that would change with the South's independence.
That change was where the money was going to go.
Slavery was the major driving impetus for the first seven Southern states to leave the Union. Not the only reason, but the major one. Had the Southern states not seceded, slavery would have remained legal in the United States for many more years to come before being outlawed or dying a natural death.