Rules of war are developed because, appalling though war is, it does not have to descend to barbarism. The recent discussion on German versus Allied atrocity should provide evidence of that.
In the West, German forces tended to follow the Geneva Conventions. In the East, they treated their foes with malice and wickedness, as sub-humans undeserving of law. They reaped a terrible whirlwind in turn.
Rules of war are less there for the war - much more in the hope of a lasting peace.
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