I believe the failure to effectively prosecute war crimes after WW1 led to the Germans to believe they had carte blanch to behave how they liked in WW2, with impunity, even after it became obvious they were going to loose. Some of the 12 indicted and tried at the Leipzig War Crimes Trials, successfully used the "I was only following orders" (Superior Orders) defence, even one who was responsible for the sinking of a hospital ship. This later became known as the "Nuremberg Defence"