In the Revolutionary War mercaneries were called Hessians.

During the War for Southern Independance Black soldiers in Union Uniform were considered as slaves in rebellion and as Traitors since there was no right reconized by either side to choose which side you wanted to be on.

White southerners who were caught in Union Uniforms were usually treated the same way and shot for the same reason, as deserters and traitors.

One such incident in Arkansas after the Battle of Marks Mill approximately 100 white recruits for the 4th Arkansas Cavalry U.S. who were captured on their way to Pine Bluff to be enlisted, were shot after that battle by their captors as traitors.

These white recruits weren't in uniform, nor were they armed, nor is there any evidence that they took any part in the battle.

Was that a Massacre? Or proper execution of military justice?