OK, so it's a "WWII What If" question, I have searched on here and cannot find an example of this being asked before, which I find surprising. Maybe my searching abilities aren't very good.
Anyhow, it's an interesting question that bears some thorough investigation, so humour me.
There are dozens of reasons why the Axis lost the war, but what if the planning and execution and just plain luck had been different?
Hitler had assumed Chamberlain would have been in charge of Great Britain and would have surrendered once France fell. Because of this he hadn't bothered to equip the Kriegsmarine with any landing craft. This meant that Operation Sealion was never a feasible option. What if he had foreseen this situation and prepared his forces accordingly?
Germany spent a lot of resources building naval forces that were never effectively used, several battleships, aircraft carriers (although none were completed two keels were laid down). What if this resource had been spent on more submarines so the Germans had twice as many in operation early in the war.
From what information I've read, Germany scaled back a lot of research and development around 1940/1941 as the war was going so well. For example their jet fighter programme on the ME262 was almost stopped for over a year, they had a prototype of this flying before the war started. Had they not been so over-confident and continued their R&D would this have affected the outcome of the war? Specifically regards the ME262 they could have had these flying in large numbers in 1943 while air-superiority over Europe was still in the balance and before the Allies could have seriously damaged their oil production facilities.
The Germans were so arrogant that they thought the ENIGMA machine could not be cracked, what if they'd been a little more humble and kept producing new encryption devices?
What if Hitler had allowed his generals to be generals rather than interfering all the time with his "no retreat" orders etc.
What if Hitler had ordered his forces to concentrate on capturing Moscow right from the start and launched Barbarossa a few weeks earlier rather than wasting time helping the Italians in the Balkans?
Hitler could have used his influence with Franco to allow German forces to transit Spain and then capture Gibraltar.
The German arms industry organised in such a way that while the competition amongst itself was healthy, it led to a situation where the German weapons, especially tanks were very over-engineered. On paper the Tiger was better than the Russian T32 in a one-on-one fight but the Russians could produce far more tanks than the Germans partly due to the way their arms industry was organised and also due to their over-engineered solutions.
What if Germany and Japan had been more coordinated, with R&D and actual combat - Japanese second front against Russia, or at least a reasonable threat of it.
What if the attacks on Pearl Harbour had been a few days earlier/later when the US carriers were in port?
Are there any WIDELY DISCUSSED theories about how the Axis might have won World War II?