We experimented with a house rule that gave the US the War Bonds breakthrough for free once they entered the war, it was no big deal to give that to them, and it was fun to see how each roll for more money turned out for the American player.
Sounds fun. I think it would be interesting to give each of the major powers a free tech at the end of turn 3. What would you choose for each power as your tech?
Germany = Jet Fighters
USSR = Advanced Artillery
Japan = Super Subs
USA = War Bonds or Increased Factory Production
China = none
UK = Radar
Italy = Improved Shipyards
ANZAC = Long Range Aircraft
France = Heck, why not give them Heavy Bombers. They won’t be able to use them anyway.