There was gallantry during the conflict and the larger armies generally observed the rules of war. However, in smaller actions the conduct of both sides was often extremely brutal.
Here’s a letter from Thomas J. Bond of the 2nd Ohio, who describes how some suspected guerillas were summarily dealt with. The letter is up for sale at HCA Auctions.
…there was a man hung on Friday and one today. It was a short distance from camp. I went over and saw him but did not go to see that [man hung] today for one was enough. They murdered a man. They cut his ears off and pulled his tung out and then cut his throat but I think they [those hung] got what they deserved…they belonged to a band of guerrillas. I would like very much to be their to attend to them pick nicker’s but it would not [have] done for me…to been to the one where Stant [was.]…I would have got in a fuss with some of the Butternuts for I hate them worse than the vilest…Rebels.
And another from a soldier in the 97th Illinois, writing from New Orleans about the Copperheads back home in the spring of 1864. It too is up for bids if you’d like to have an authentic letter.
I was very glad to hear …that Mr. Sturgis had abandoned the notion of going into the service again…[and that] there had been some Copperheads killed by the soldiers in the county. I was glad to hear of that. It serves them right. I would rather kill a Copperhead than a rebel…the news from old Grant is glorious…Richmond will fall this time and the rebs be driven from Virginia …Grant can do up the job if any body can…
As Sherman put it, “war is cruelty and you cannot refine it.”