Oooh! I wanna play!
Here are a couple of errors that I think have been somewhat overlooked:
Germany’s re-arming of the Rhine: In 1936, Hitler pulled his first and most risk-laden ballsy move. He reoccupied the Ruhr and elsewhere along the western German borders. The troops were sent in with unloaded weapons, just in case the French decided to come in and reoccupy. Any sign of conviction on the part of the French would have exposed the German army as the paper tiger it was at the time, and the entire war might have been averted (temporarily).
The invasion of Poland: Many sources are of the opinion that Hitler genuinely underestimated the resolve of Britain and France, and was suprised when they honored their alliance with Poland. It threw off Germany’s timing for the whole war, particularly for the Navy, which was planning for a conflict beginning sometime in 1943-44. It also spiked German plans to move over to an all-mechanized Wehrmacht (which the British and Americans were both converting to) and forced them to stick with the horse-drawn army for the duration.
French ineptitude in the Saar: While the Germans were throwing everything they had at Poland, the French crossed the border into the Saar. Unfortunately, the counterinvasion completely fell apart in the face of scratch German resistance. Had they pressed the attack, they could have quickly headed for the German industrial areas and severely crippled Germany.
The invasion of Crete: In addition to something like eleven divisions being tied up in the Balkans just prior to the German invasion of Russia, Germany also shot the wad by sacrificing the elite and highly mobile XI Corps, the airborne Falshirmjaeger, just when they could have come in handy in Russia. Furthermore, the loss of high numbers of Ju-52 transports in the mission made air-supply of German troops in Russia a practical impossibility.
Finally, there is an interesting bit of revisionist history in the works that, if proven true, will give a slightly different cast to the Battle of Britain. According to Viktor Suvorov (Vladimir B. Rezun), the Soviet Union had spent over a year and a half quietly but deliberately preparing for an invasion of Germany in July of 1941. There is some evidence that the Germans were aware of this, and were therefore really pushing for a cessation of hostilities with the U.K., be it by invasion or otherwise, at an early date. I think this further underscores the resolution of the British people at this trying time–the Germans threw the kitchen sink at them, and failed.
Here’s a review of one of Suvorov’s more recent works:
http://www.stv.ee/~flylow/review.htm