It's to make the game challenging when you play as allies on historical. Problem is that it really screws you up when you play as China or the UK. As China you stand no chance playing historical because the Germans will come and the U.S.A AI will not help you. Playing as UK feels unhistorical because you end up doing it all yourself.
For the majors, playing as Germany, Soviet Union can be a great game on historical. As the allies you HAVE to play U.S.A because their AI just cannot set up a second front efficiently but also spreads its fleet up into small chunks which the Japanese AI seems to do a great job of crushing. The U.S.A troop transports seems to be weird also. They seem to ship around and around in circles without actually ever doing anything.
It’s probably my only major gripe, give me a U.S.A AI that can win historical WW2 maybe 75% of the time (to make it interesting) and this game is near close perfect.
Yes there are other bugs but a better U.S.A and a little Allies AI would help leaps and bounds.
HOI4 has come so far since release.
