Hitler made some decisions that changed the course of history.The Nazis found out about an atom bomb but they did not give them the money to build on and to mass product a faster airplane than the allies.
The WWII German atomic bomb project was a joke. Not only had Heisenberg screwed up the calculations for how much uranium was required, but he had also been completely wrong about the reaction itself. If the project had ever proceeded the ensuing nuclear accident would have killed virtually every scientist involved, and irradiated a good swath of Germany. As for the Swallow, speed isn't everything, and it couldn't do much beyond go fast. The engine was made of shitty materials (because Germany didn't have access to the higher quality ones) it could only operate for something like 300 hours, total, before having to be replaced.
Anyhoo, to the OP. Basically the main problem is the same as happens in any alternate WWII scenario. The answer can be summed up as "the United States takes its other hand out from behind its back." America has such a massive lead over EVERYONE in industry and production that simply having it on one side gives said side an overwhelming industrial advantage.
Even allied to the USSR Japan will not be able to win in the Pacific, because the Soviets can project no power in the ocean, which is where Japan desperately needs help if it wants to win.
Meanwhile in Europe his alliance is incapable of striking at the UK for a similiar reason, leaving the Allies able to build up an unassailable position of strength right on the doorstep of their foes. The opposite is not true. There is no position in the Americas to threaten the United States, nor can one be developed.
The end result is probably either nuclear annihilation of the ATL-Axis, or the Allies blocking Europe from international trade, while fighting low level conflicts against them in the Middle East and Asia.