OzzyKP
Emperor
Dont try to replicate history
An united america has no reason to enter either world war
indeed without an American government seeking to control china there is no reason for its intervention in the second at all.
France, Britain, Spain and Germany are enough foreign powers to be going on with, as America never had anything to do with the orient untill well after its debubt as a world power.
I would suggest that the best place to set it would be the year of the Civil War only with the north having volunteerily given the south its independance, so very frostly relations between the two but no war.
For this setting and inclusion of the Revolutions mod might work quite well as a disunited America without an all power federal army would be prone to instability.
I don't see how it would unfold that the Union would allow the South to sucede peacefully. It is just too important a part of the country to not fight over it. An important piece of this will be the fact that the North and South will start the scenario at war. Both nations will be much bigger, more populous and better developed than any of the new, western nations. The only way the western nations can get some breathing room and get a chance to develop would be if the two big nations start at war with each other and keep each other bogged down. Plus 1851 works better since the two halves would be more equally matched than they were in 1861.
America had a huge amount of contact with China & Japan during this period.
For China:
http://en.wikipedia.org/wiki/Open_Door_Policy
For Japan:
http://en.wikipedia.org/wiki/Japanese-American_relations#Commodore_Matthew_Perry
The opening of Japan was definitely a big deal. We helped westernize them and by the end of this time period Japan was a world power in its own right. Plus Chinese immigration was a huge factor out west and contributed to the construction of the railroad. I was hoping to use that as a mechanism. Plus it is likely that west coast nations like California would have more incentive to trade with and partner with Asian nations like Japan and China.
I think some diplomatic options would be unavailable for Japan and China at the start of the game - like blockades and military assistance - but they could come in as the game progresses. It would be a good mechanic to have where some civs rise and the diplomatic situation is forced to change to accommodate it.
As for Vermont, they were an independent nation for 10 years during the American revolution. So it would be entirely appropriate to keep them in this despite the difficulty they'll have at staying alive. I think they will seek out vassalage by either Canada or the United States for survival, which I think would also be appropriate.