The Federal generals didn't seem to have read the 1863 guide for behavior of the Union army in the field. From article 16 of that document, which was issued by Lincoln:
Military necessity does not admit of cruelty -- that is, the infliction of suffering for the sake of suffering or for revenge, nor of maiming or wounding except in fight, nor of torture to extort confessions. It does not admit of the use of poison in any way, nor of the wanton devastation of a district.
What is a source for this?
Walt
I'm not sure what you're referring to here, specifically. My impression is that Sherman and others decided to fight their campaigns by living off the countryside, rather than trying to extend and protect supply lines that were subject to attack by cavalry and militias. If a city had military value, say as a fort, then that value had to be destroyed. But I seem to recall that the confederates burned Richmond.
Since you brought up field regulations, would you agree that men in uniform, regardless of race, were entitled the same status when captured?