if both japan and germany wanna try to take USA,that maybe easy though you face an human player.
you should look at my germany's taken the whole north america in 1942
Yes, I could do that too if I edited the unit combat capabilities table. [;)]
Now granted, you might have actually conquered the US as Germany in 42 through some AI exploit everyone else is unaware of, but I think its just as likely that you modified the combat values of all of the WA units so battleships would lose to your transports.
No way you do that against a human player. It's just not going to happen.
I'll play you a game and you can prove me wrong. In fact I will not build any additional troops in the US until you unfreeze them.