@Cernel said:
For example, the restriction can be that the US cannot invade any enemy territory so long as any part of the US plus Hawaii (so not comprising Alaska) is in enemy hands. This way, while going for KGF, the United States is forced to do the minimum necessary to keep Hawaii (need splitting it in more than one island to avoid this being done just by piling up land defence, or you can add that also warship presence near the West Coast counts as a no-no as well). Not a big fan of political restrictions though.
Sounds like an obnoxious rule to play with, and it still wouldn't compel the US to do anything beyond stacking defense in Hawaii - they can still hang China, India, and Australia out to dry while dogpiling Germany.
I would continue to look at the bonus objectives as the right way to incentivize a mixed strategy. Besides messing around with Germany and Japan's bonuses to make them more dangerous if left unchecked, there's an alternative option, which is to tie the US objectives to sets of goals located in both the European and the Pacific theaters. And not just little ones. If the US is still getting something like that big 30 IPC bonus from Global 1940 just for being at war, break that bonus up into chunks, say, three bonuses worth 10 IPC each.
Match each of those 10 to a target in the west and a target in the east.
For example:
10 if the Allies hold both India and London
10 if the Allies hold both Canberra and Egypt
10 if the Allies hold both Hawaii and Moscow
The bar should be set pretty high for the Axis, so the targets should be objectives the Axis never actually managed to take in real life.
But you see what happens if the US ignores one theater now? Germany or Japan have the opportunity to slice a huge chunk of income away from the US player. The Axis dominating either theater reduces US power across the entire globe, so the US player must commit to fighting both.
Your economies have much different base values from the vanilla G40 game, of course, so you'd have to adjust accordingly to account for the relative difference.