Actually blacks did fight alongside their white counterparts. There is adequate proof on the web to prove it. Some names to look for Douglas, Forrest, Grant and Lincoln. It is A proven fact that all but one Mississippi unit had blacks serving in combat roles.
Also read the EP you which only freed those slaves in rebelling states. How about the original 13th amendment? To maintain slavery, indeed sounds like you want to add you spin with factual backup.
GP