What do you think the result would have been had Germany and Japan worked much closer together ? Instead of Japan attacking America and Singapore they could have attacked Russia and forced them into a 2 front war. America would have no reason to declare war on either nation until much later. They could have divided Russian territory. The Japanese everything East of the Urals and Germany everything in the West. Being busy with the Japanese Russia could not have used troops from the East to stop the Germans at Moscow or even the next year at Stalingrad. Plus it would have been much harder for the USA to send help in the form of rolling stock and other supplies. The only port available then being Murmansk and Archangel. It also would have been more difficult to transfer factories in the Ukraine to East of the Urals.