I have found it’s still very difficult for Germany to survive if Russia, Britain and USA team up.
The primary reason for this is the difficulty in sustaining a German navy. Even at 6 IPC each, subs are expensive when you need to buy tanks and fighters every round.
That being said, I won my first game playing the Axis. I was aided by my opponent’s poor play as he ignored Japan. My Japanese units conquered Western USA, Central USA, Mexico, Western and Eastern Canada and it was over.