I have researched genealogy in East Tenn. and N.W. Arkansas.
These two areas had much in common - mountainous, non-slave owning, many descendants of Rev. Wart soldiers.
In NW Ark, you find many veterans of the were who were enrolled at times in BOTH armies. This was a matter of self-preservation.As first one army, then another occupied your area, you had to practice duplicity or see your home burned and perhaps your family murdered.
I am sure commanders on both sides were a bit suspicious of the degree of loyalty to their cause of recruits from these areas.
Over 100,000 Tenneseeans were in the Confederate Army but 40,000 were in the Union army. Propagandists for the "lost cause" did a good job after the war of keeping southern disunity a secret. The federal government did little to sustain the southern Unionists either.