You're mistaken. Blacks did fight for the Confederacy. The South didn't just fight for slavery. Yours is the popular myth. The South fought the Civil War for the same reasons they almost didn't stay part of the Union after its founding. Political, economic, and social differences between the North and South were plenty of reasons for secession. Slavery was only one part of the total concern.
Any blacks "fighting" for the Slavers were a tiny number although there were plenty of valets for the aristocracy, ditchdiggers, cooks, teamsters etc. When United States armies appeared ANYWHERE in the South they were inudated by slaves trying to escape the Tyranny of the Whip and the Lash.
Of course, the Slavers provoked the RAT Rebellion over slavery that was what they said themselves not just me. NONE of the other concerns would have provoked a decade long conspiracy to secede. There was no "tyranny" and the Slavers did not even wait until Lincoln took office before attacking the US.
There was NO "almost didn't stay part of the Union after its founding" except in your mind. And the South controlled the federal government for almost the entire period prior to the RAT Rebellion.
But these threadbare falsehoods are all the DS's have to try and defend the indefensible.