[Friedrich H]

Being born, in the first place, I'd say…

But it would have to be the decision to invade the Soviet Union and then declaring war upon the United States.

Surely his biggest mistake was the one of not following the advice given by his generals. He repeatedly, and near the end constantly, countermanded the advice given by experienced men on tactical and stratigic advice

Just because you are the boss doesn't mean that you know better than your advisors. It does however mean that you take the can for any mistakes if you ignore their advice.

This has many things of a myth, actually. All this thinking was created by Sir Basil Lidell-Hart in the 1950s by interviewing many German high-ranking generals who blamed all their failures on the mad Bohemian corporal.

The truth is different, nonetheless. Hitler never took decision unadvised and sudden decisions (on the contrary, he delayed decisions on critical affairs till they reached moements of utter crisis!). As War Lord, Hitler was not the military genious he himself thught he was, but he was not the incompetent maniac many believe he was. He actually had a very wide (perhaps too wide) strategic view of things and a very sharp tactical sense.

Hitler practically invented the glidder airborne concept, he came up with the idea of the lighning attack on Norway, he supported innovative generals such as Manstein and Guderian in 1940 against all odds, he saved the Wehrmacht in 1941 and again in 1943.

But, of course, his mistakes had far deeper consequences and his defeats were much greater than all these successes.