There is a simple truth here: War is horrific, and that is why it should always be a last resort. It can strip the humanity from the best of us. And give rise to monsters in the worst.
In wartime, there will always be a propensity for these sorts of atrocities. Acts of unspeakable cruelty have been documented going back hundreds of years, from the Japanese practicing tamishigiri on live prisoners, to Conquistadors flaying the genitals off of Mexica women. And a few American troops have done similar things over the years, but it has never been widespread.
The difference lies in the prevailing culture of the armed forces. If the culture utterly dehumanizes the enemy -- like the Germans or the Japanese, or the Conquistadors, Crusaders, Inquisition or Intifada-- the atrocities will be on a much vaster scale.