But this assumes the US never entered the war. The US was basically invincible before the advent of the ICBM because there was no way for neither Germany nor Japan to launch an effective attack on the US mainland, and more importantly, on its industrial capacity. But the US could easily attack by air both Germany and Japan thanks to allies within striking range. The standard Nazis/Japan conquers the US scenario as in The Man in the High Castle just doesn't make sense.
If Germany had not invaded the USSR then they would both have had the upper hand at an invasion of the British Isles and an allied invasion of Europe would have been close to impossible. At which point whether Germany could successfully invade the US becomes irrelevant because neither side can destroy the other, which usually leads to peace talks and a peace agreement that acknowledges the status quo, which was German control of Europe.
Again, that's not very different from the situation in 1812. In fact Germany had a much stronger position.
Japan also went way over their heads but they actually did that early when they invaded China. The attack on Pearl Harbour was the nail in the coffin because that led to full support from the US to China along with destruction of Japanese industrial capacity.
Don't try to invade Russia, and don't try to invade China. This may sound obvious but history shows that lessons need to be learned and re-learned the hard way.
