Those hanged were deserters from the Confederate army who joined the other side and started fighting against their former comrades. After they were captured by the Confederates, they were hanged by order of court marshal.
From the Richmond Dispatch newspaper of February 19, 1864: [Source]:
More Executions of deserters at Kinston.
--The execution of seven deserters at ← Kinston, N. C., on the 13th, has been published. On the 16th thirteen more were banged [sic]. The correspondent of the Raleigh Confederate. says:
J. S. Brock, Wm. Haddock, C. Huffman, Stephen Jones, A. J. Britton, J. I. Sumerien, William H. Daughtry, Lewis Taylor, Lewis Freeman, and Jno. Freeman, of Nethercutt's battalion; and W. D. Jones, of Wright's battalion, and Jos. Brock, of the 27th N. C. regiment, and C. R. Cuthrelt, of Latham's battery, were all hanged in this place on yesterday, by order of court martial, for deserting their comrade and taking up arms on the enemy's side. They all received the ordinance of baptism, according to the dictates of their own consciences, on the morning of their execution. Two were baptized by immersion by the Rev. Mr. Camp, of the Baptist Church, whilst the others were sprinkled and poured by the Rev. Mr. Paris, of General Hoke's brigade, who were their spiritual advisers at the gallows.The prisoners were accompanied to the place of execution by a large concourse of people, both citizens and soldiers, with a strong military escort.--They ascended the scaffold with a firm and elastic step, and met their fate with much fortitude and determination. The ropes were all suspended from the beam of the gallows, and Stephen Jones and Wm. H. Daughtry selected the once by which they preferred to be hanged.
I am informed that three more deserters are to be hanged here in a few days — making in all 23 within the last two weeks, all of which were captured by our troops in the late expedition against Newbern. Old or Haddook, father of the Haddock who was hanged here yesterday, and his son, were arrested for some cause, and brought to this town last night and lodged in the guard house.
Perhaps you are familiar with US Military Law [Source]:
Any person found guilty of desertion or attempt to desert shall be punished, if the offense is committed in time of war, by death or such other punishment as a court-martial may direct, but if the desertion or attempt to desert occurs at any other time, by such punishment, other than death, as a court-martial may direct.
Here is what General Grant thought [Source]:
Grant disagreed with Butler's argument, as he had indicated in an earlier letter to Confederate general Joseph E. Johnston regarding Confederate deserters who had joined the Union army. "Of course," Grant had written, "I would claim no right to retaliate for the punishment of deserters who had actually been mustered into the Confederate Army and afterwards deserted and joined ours." He did not agree, however, to punishment for Union soldiers who had been conscripted but deserted before being sworn into the Confederate army. Although Elijah Kellum fell into that category, this exception would never be seriously pursued by Union authorities.
There is a long discussion in my last source above about attempts over the years following the hangings to charge and try Pickett for them.
But the point I was trying to make is it was a mass hanging. Which means that the claim that the execution of the Sioux was the only mass hanging in American history is wrong. Correct?