What was the biggest mistake made during WWII?

[Peter666]

The first major German mistake was not finishing off the allies at Dunkirk. They allowed 300,000 men to get away. They followed this up with the Battle of Britain failure which put the war on two fronts. If they would have routed the allies at Dunkirk, they could have settled with Britain and focused on the rest of mainland Europe and Russia.

Their invasion of Russia was not a bad tactical move if they had first avoided a two/three front war and secondly had not committed atrocities against civilians. Many Russians and Eastern Europeans were gladly willing to fight the Soviets, but after experiencing the German atrocities (such as burning of villages in Belarus and murdering their inhabitants) they joined the Soviets. Very stupid "Arian superiorty" and they got what they deserved.

On a side note, most people don't know that many of the "Germans" defending the beaches on D-Day were actually Russians who had joined the German Army!