Besides the long title, it’s been a question poised a dozen times with different answers every time.
Starting from September 1st, 1939, what is the fastest possible way for the WAllies/Soviets to defeat Nazi Germany?
This does not require unconditional surrender, but that would help. A Franco-British attack over the Maginot line, perhaps? Some way to get Belgium and Holland in the war early? Convince the Soviets to break the NAP? What could possibly work, or do the allies need the time given to them OTL to prepare a counterattack?