I would reckon it’s something akin to The Posse Commitatus Act, ie use of a military force against predominantly civilian population.
Much as I reall really hate Sherman Tecseh Grant, he was right on the score bout one thang: War is hell.
With that being said, civvie casualties are highly unprofessional still .
Yep. Sherman said you have to make war so horrible, that no one would ever want to engage in another one. He also said you have to take the war to the people (civilians), because they are the ones supplying the troops, and giving them the ability to continue fighting. You have to break their will to fight.