Incoming long post... I'll try to keep it succinct.
When the AI is left to its' devices in Europe, Germany and Italy get rolled... hard. About turn 60 or 70, it starts to collapse completely to the point of no return. If Japan doesn't come to the rescue before then, Russia can be defeated... but the UK is entrenched with so much supply and massive air power that I had to give up after turn 160. I was on Berlin's doorstep but I had stalled b/c I couldn't counter the RAF.
Conversely, when the pacific war is left to it's own and I played Germany... Japan struggles to beat China and the USA does get involved, mostly around Manila and Guadalcanal. But the naval battles are lackluster... Japanese carriers get encircled by the US but the only naval unit that seems to attack them is subs. Japanese use air power to go after destroyers and seemed to do so effectively, even though I would never have done that
I think ultimately, America needs to get involved in the war in Europe. They require something to draw the AI to deploy air/ground and naval ground forces from mainland US into Africa and/or Europe. I don't have a great understanding of how the AI works, but if the yanks had a city in the UK... would the AI deploy to protect it much like they do Manila in the pacific? Certainly the AI would base aircraft there, which would be a major improvement, especially with the strategic bombing/improvement pillaging that bombing causes.
The AI has been using strategic and tactical bombing and it could be an effective strategy, but only if the USAAF gets the urge to deploy there.
I know that would be a complete fiction... the Americans certainly didn't own any bases in the UK during ww2:
Can we give the AI victory conditions or objectives (namely for Canada and USA)? Would that motivate them?
It's bizarre... late war (turn 140+), I'm seeing Cuban destroyers helping out in Europe... but STILL no yanks!
Faster embarked movement might be helpful, but I'm cautious about making transports faster than naval ships. Maybe a blanket +1 speed for all seafaring ships?