It seems strange that, although Japan and Germany were allies and both were sworn enemies of Russia, they never coordinated their attacks. Japan took advantage of the war in Europe as an opportunity to grab colonial territory but it never really did much to help Germany. (Bringing the United States into the war by bombing Pearl Harbor certainly did not help Germany.) There was never any coordinated strategy.
I believe this is the major reason they lost the war.
Interesting what if Germany didn’t declare war on the US.
I still suspect the US basically would have simply heightened their shipments to Britain, and the moment any of our ships were attacked, that would have been the Casus Belli, and we would have declared war on Germany anyway, probably within the next few weeks at the most.