o DUNKIRK - as a "gesture", Hitler held back in capturing the BEF. If he had not done so, English morale would have suffered a tremendous hit, not to mention the loss of experienced troops.
o BATTLE OF BRITAIN - if the Luftwaffe/Goering had seen the destruction of the RAF airfields all the way through and gained air supremacy, things would be grim indeed for the Brits. I believe the guy who "really" saved England was Bomber Harris, who launched a bombing raid of Berlin when things were at their grimmest. This bombing raid attacked German *civilians*, and caused both Hitler and Goering to lose face, but the result was to take the Luftwaffe out of their gameplan and start bombing the British cities in retaliation, giving the RAF airfields and radar installations badly needed respite (the British civilians had to bear the brunt of course, but they did it with typical British aplomb).
o BARBAROSSA - if Hitler had postponed the attack on the Soviet Union, he probably would have had an easier time of it against the Brits. The Soviets were unlikely to take on the Germans until/unless the Germans were already on the ropes.
o DECLARING WAR ON THE US - if Hitler had not declared war on the US, it is not clear the US would have declared war on Germany...imagine Hitler denouncing the Japanese and in a very public way saying it was willing to help the US defeat Japan! (imagine the effect on US public opinion particularly given the German/Italian/Irish population which was inherently anti-British)
o THE BALKANS - if the Italians had been able to take Yugoslavia by themselves, the Wehrmacht would have had many more soldiers and assets to use against the Soviets and Stalingrad could have had a very different outcome.
o ME262 - if Hitler had not tried to turn a fighter jet into a bomber, the Luftwaffe might have been able to stem the waves of bombers against the German heartland.
As to those who say that taking Britain/Scotland wouldn't have changed the outcome of things, perhaps and perhaps not.
Gibraltar probably would have fallen. The great convoys would probably not be able to get to Murmansk. The nightmares would have started to pile up in a hurry...
the list goes on and on... just a few of these might have lead to a very different outcome -- it looks like God was helping out in this one!
And a lot of good people either slacked off on their duties under Hitler (Heisenberg?), and a lot of even better people made sure they were on our side of the front lines before the war started.
o DECLARING WAR ON THE US - if Hitler had not declared war on the US, it is not clear the US would have declared war on Germany...imagine Hitler denouncing the Japanese and in a very public way saying it was willing to help the US defeat Japan! (imagine the effect on US public opinion particularly given the German/Italian/Irish population which was inherently anti-British)
o THE BALKANS - if the Italians had been able to take Yugoslavia by themselves, the Wehrmacht would have had many more soldiers and assets to use against the Soviets and Stalingrad could have had a very different outcome.
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I recently read a book on famous strategic mistakes throughout history, and all three of these made the list. First, Russia and the Balkans. Hitler had originally planned to launch Barbarossa earlier to avoid the Russian winter that had stymied Napoleon, but was forced to divert to Yugoslavia to save Mussolini. Oops.
And then, there's Japan. The Germans were caught as off guard as anyone else, and were much relieved the next day when Roosevelt asked for a declaration of war against only Japan. The idea of going up against a force which could "sit back for years and build up a massive force which, once unleached, would be unstoppable" was unthinkable. And apparently Hitler didn't think about it.