Umm, they dissolved their partnership with the states. - hint "United" STATES of America. They left and became the CSA.
And southerners didn't call it the war of northern aggression on a whim. All of the early battles were Union troops attacking CSA territory.
Perhaps you didn't understand the crude analogy. Sure, slaves were "cheap" labor at $1000 or more a piece, but the slavers viewed slaves much the same way a farmer today views a piece of machinery - an investment - a slave cost more than a white field hand would make in 5 years.
You might find it hard to believe, but some slave owners would go broke and sell off the slaves to recoup the losses.
The difference between a tractor today and a slave in the 1800s was that you bought 2 slaves and they multiplied, and the new offspring slaves were free labor. But it wasn't like a farmer just went out and bought a few slaves and watched the money roll in from free labor.