Do you like historical "what ifs?" Here's mine.
Hitler took his eye off the ultimate prize, conquering the Soviet Union. Hitler needlessly and detrimentally went to war with Britain.
Upon taking France, Hitler should have disarmed the French (as they did), dismantled the Maginot Line and then announced that it was unilaterally withdrawing from France and state that they never wanted war with the allies and that their territorial claims in Poland were just. The French would have retained their navy (as they did anyway) and their colonies. I'm confident that the French would have readily accepted such generous terms from the Germans.
Hitler would have refrained from invading Denmark, Norway and north Africa while also refraining from any attacks against the U.K. Politically speaking, Churchill would have had virtually nill support for engaging in war against the Germans considering that the French were out of the war and at peace with Germany and considering that the Germans were not taking any aggressive actions against the U.K.
Hitler also would have needed to NOT declare war on the U.S., as he was apparently bound by agreement with Japan to do.
Had Hitler done these things, Germany would not have been at war with the western allies. He would not have expended and wasted massive resources engaging in needless wars in the "Battle of Britain" or in north Africa nor in occupying and fortifying France.
There would have been no British and American bombers bombing Germany's infrastructure. It's quite possible that American aid to the Soviets would never have happened or that the support would have been significantly less.
Hitler could have had the one-front war that he always wanted and have gone to war with the Soviets without having one arm tied behind his back, so to speak.
I will also add that Hitler's desire to actually take Stalingrad was completely unnecessary and counterproductive. He didn't need to take that city. They could have taken the oil fields in the Caucasus oil fields.
One glaring omission was Hitler's genocide of the Jews. Obviously, this would have been problematic for Germany in the long-term as the western allies, sooner or later, were going to learn of what was happening and would have responded with war. Hitler could have delayed his war against Jewish people in order to focus on winning the war. Thereafter, he could have advocated for the state of Israel and then worked on a program to humanely send European Jews to the newly created state.
Hitler would have needed to take Leningrad and then fortify western Russia and the Ukraine in order to be able to retain his conquests. The Germans were never going to be able to take and keep Moscow or Stalingrad. The Germans simply could not won the battle of attrition with the Soviets over the long-term.
Here is what "winning" the war would have looked like for Germany.
1) Defeating the allied armies in France, disarming the French and then making peace with the allies and, of course, avoiding war with the U.S.
2) Seizing Leningrad, the Ukraine and the Caucasus oil fields and being able to hold those territories.
3) Avoiding genocide of the Jews by, instead, exporting Germany's Jews to Palestine or a newly created "Israel".
Still, the Soviets would not have taken this lying down and the idea that the Germans could have, in the long-term, been able to retain control of their territorial conquests in the east seems unlikely.
Thoughts?
