My observations
United States -- way to easy to get the USA to join alliances. It should be virtually impossible for the US AI to join any alliance, especially with European powers, as the US was extremely averse to any involvement in continental affairs at the time. Only very late in the game, such as after 1905 or 1910, should there be any kind of possibility the US will ally with European powers. Currently, the alliance value of the base US 1836 and 1881 AI is 0, which is normal tendency to form alliance. It should be kicked up to 120 or 150, extreme isolationist level, and only come down by event.
I also suggested in the North American VIP thread that the USA needs several switching AIs to handle its shifting priorities during the game. My thoughts are in general:
Base 1836 AI -- extreme isolationism (150), Monroe Doctrine protect priorities in Western Hemisphere, research concentrated on commerce and industry, railroad buiding in the Northern US, small military builds. Industry AI focuses on fabric, glass, paper, furniture, and clothes factories.
Mexican American War AI (activated by MexAm War event chain, or other war with Mex)-- extreme isolationism, emphasis on destroying Mexico set as high as possible (100), AI targets Mexico City province for capture to increase likelihood of triggering VIP Guadalupe Hidalgo event, increased military builds. Tech goals switch to more military oriented. AI deactivated by treaty of Guadalupe Hidalgo and successful capture of American Southwest/California
Antebellum AI (switched to after MexAm War) -- extreme isolationism (150), research priorities return to commerce and industry. Factory and railroad building more of a priority, and increased weight on building steel, machine parts, heavy industrial factories.
Civil War AI (switched to by Civil War event chain) -- lessened isolationism, but Monroe Doctrine protect priorities slip as attention devoted to domestic fighting. Emphasis on destroying CSA/fighting to bitter end set high (100), and AI province targets set to the four provinces that trigger end of Civil War and reunification -- Richmond, Nashville, Atlanta, New Orleans. Military builds greatly increased, as is research. Military builds tweaked -- no more European style units like dragoons, just cavalry. Target countries to befriend include ENG, FRA, PRU, and RUS -- the first two to head off CSA diplomatic efforts for allies, and the second to secure potential allies if needed.
Reconstruction AI (triggered by end of civil war, lasts until 1890s) -- return to extreme isolationism. Military size reduced, commerce, industry, and now culture techs become priorities. Tweak industry and railroads to simulate building of historical industries and transcontinental railroad routes.
Expansionist AI (comes around 1890) -- the beginnning of American involement in the world. Still very hestitant to form alliances, probably set at 110 now, but there is some chance. Enemy target countries set to SPA, and target provinces include Cuba, Puerto Rico, Phillipines, Hawaii, etc. Also increased interest in China. Naval research and builds increased.
World War I AI (activates 1913, like the others) Sets priorities for WWI and increases chance US will join an alliance, reducing the alliance setting to probably 50 or less. The allies will still have to work it, but eventually the US will come.
Anyway, these are just some quick thoughts on how I think this key country's AI should be handled. I saw in another thread that there is a group that is looking at making these multiple AIs, and I would like to volunteer to work on the USA/CSA set once 1.03 comes out and we see what changes have been made.
Probably from waaayyyyy too many test games of CORE. I'm hoping to be able to use that knowledge for Victoria, and reduce my learning curve. that all said, step 1 is to identify the problems, step 2 is to declare colonial war, and make the see the light. 
