World War II, the greatest conflict which humanity has ever endured, was a culmination of immense political, historical and nationalist forces. The year 1941 marks the point where it transformed from what was then just an expansive war, in which Britain faced its greatest challenge in centuries, to a true global conflict.
There were plenty of points where it could have begun, or escalated earlier - The French or British could have taken a harder line against Germany, the Soviets could been more aggressive and launched a pre-emptive invasion of Germany, or America could have gotten into the war of its own initiative in either Europe or the Pacific. However, pushing the date later seems much more difficult. That's why this is a challenge.
Challenge: With a POD no earlier than 1937, ensure that no full-scale world war begins before 1943. Large conflicts that will eventually feed into this are still allowed - for instance, the Sino-Japanese war is pretty much a given, and it's unlikely that Europe can remain at complete peace for the whole time, but peace, or a "phony war" equivalent, must last until at least 1942, and the Soviets and Americans must both stay out of the war (at least officially) until 1943.
Also, how would this affect the course of the war.
Technology would be a big factor, as all the power would be investing heavily to prepare for a conflict they could likely see coming. The assault rifle would play a major role for infantry. Rocket technology would be more advanced. Well-developed long-range bombers would be present from almost the beginning of the war. Tank technology is ahead too.
Tactically, it seems likely that Japan will be in a better position with more time to consolidate in China. But then again, it might fight with a very different strategy - blitz through Burma perhaps - assault Siberia?
Even Italy matters here, believe it or not. Well, maybe.