There wasn’t really a large number of blacks who fought for the Confederacy. I’m excluding in my statement those people with African descent who passed for white or considered themselves/were considered white…people like Randall Lee Gibson, who was a Confederate General and later Representative and Senator from Louisiana, who had, unbeknownst to him, black ancestors.
There were, according to Harvard professor John Stauffer, 3000 blacks in Confederate military service, most of whom, slaves of white officers who defended themselves or their masters in the heat of battle. This was, under Confederate law, illegal, and the Confederate Congress and Department of War didn’t actually authorize any black troops until the last week of their existence, at which point, it was pretty much moot.
The only actual black Confederate unit was the Louisiana Native Guards, made up of free blacks from New Orleans who, in a patriotic gesture, volunteered. The Confederate government never got around to actually accepting their service or issuing them weapons, and then when New Orleans fell to the United States, the Native Guards volunteered for service in the US army, becoming, on September 27, 1862, the 1st La Regiment, Native Guards, which has the distinction of being the first black regiment in the US army. (Take that, 54 Mass)
As for the Native American question, you’re right…the last major Confederate force to surrender was Stand Watie’s Cherokee Confederate unit.
Considering the ‘black confederates’ thing is pretty much just a myth (a handful of names and, few slaves carrying hunting rifles, and some slaves put into uniforms because of the convenience of clothing is pretty much it) I really don’t consider their reasons for fighting to be of much concern.
Percentage-wise there were probably more blacks in the German regiments during the Revolutionary War than fought in the Confederacy
Its sufficient to say that the Japanese were never really punished for their war crimes like the Germans and they never really acknowledged them the way the Germans did. I suspect that China will have something to say abot that on a going forward basis.