When should Germany have surrendered?

[D-Day_Dodger]

I pretty much agree with Grumbler's comments. The day Hitler declared war on the USA was the day he sealed his fate. At the time of Pearl Harbor America was overwhelmingly isolationist (about 80% is a figure I've read). It was an incredible act of hubris on Hitler's part and showed his glaring ignorance of America's potential to wage war.

I have no doubt that Roosevelt wanted to enter the war and come to the aid of Britain. Strong arguments have been made that he manipulated the Japanese into attacking America as a means of accomplishing this goal. However, the attack on Pearl Harbor did not guarantee this. America would not have gone to war with Germany without some serious provocation. Even though Germany had a tripartite alliance with Italy and Japan this did not obligate the Americans to declare war on Germany or Italy. Hitler should have told his Japanese allies, "Sorry guys, you're on your own". But once war was declared Roosevelt identified Germany as the main enemy and directed most of America's resources to the defeat of the Nazis.

From a military point of view I firmly believe that Hitler lost his best chance to win the war when he let Britain rescue 300,000 of its troops from the beaches of Dunkirk. If he had forced these troops to surrender Britain would have either negotiated a peace or been ripe for invasion.
With Britain out of the war the British Isles could no longer be used as a springboard for invading the continent. With his western flank secure he could have moved most of his troops from the Western Front to the Eastern Front for the invasion of the Soviet Union. These extra troops could have tipped the balance against the Soviets in the first critical year of the war against Russia.