Holocaust was absolutely horrible. What really gets glossed over is the same thing was done by the Soviet Union (our "ally" in WW2), but on a much larger scale. The largest concentration camp during WW2 was a Soviet gulag. Soviet soldiers who surrendered to the Germans were sent to the gulag after the war for committing the crime of not dying in battle. The Soviet Union invaded Poland shortly after the Germans did. Despite this, no declaration of war was made on them. I could go on, but the worst offense was Soviets sitting in judgement during the Nuremburg trials after having been responsible for similar atrocities.