Whew. That's a lot of ground to cover. Just to forward to folks and write it to get it down (and accepting all of these have the hanging 'Final Countdown' debate over whether active intervention or not is a good idea)...
-USSR: Stalin is going to go full paranoic again, and with the US nuclear program and others that were under Soviet observation and infiltration gone...Well, the information-gathering side of things is going to have to be reformed from modern folks sympathetic to the guy. And even the vast majority of leftists in the US are hostile to 'tankies' of whom Uncle Joe is the premier example. This is one that might be 'Operation Unthinkable is going to have to be a thing' as a situation, in the name of not abandoning half of Europe to the folks, a laughably absurd difference in military capability, and the fact that it's quite plausible Stalin would try something himself in an attempt to win Europe in a fait accompli before the new-America can settle on any course of action (none of which really are good for the Soviets). Especially since the US is going to have modern forces popping up in Soviet-occupied Poland and Hungary that would probably experience a shitshow of someone's making.
-China: The other big-name flareup. The US is going to be in a position to do something about the ongoing civil war and have the prospective of saving literally millions of lives lost from war, famine, and the like. But supporting Mao is...unlikely...and Kai-Sheck is not a good alternative by any means. And with the host of other shit to do, trying to logistically support some kind of 'humanitarian' expedition seems like it'd be a stretch (and violate that old maxim against a land-war in Asia).
-Korea: Actually might sort out well? The US deployment on the DMZ is larger than the US forces there in 1945, and thus should be able take over for the Japanese occupation more quickly and effectively, would presumably have a good bit of experience in Korean language and customs at least (if not outdated...or...indated? future-dated?), and would probably be more helpful and accepting of the Provisional Korean government than Hodge was (and a quicker tossing-out of Japanese might help with the civil unrest). Best-case, the division never really takes hold and the peninsula as a whole organizes a government under UN (sans USSRY likely) observation/endorsement in '46 or '47 since Soviet propping-up of the northern sections never has a chance to take hold.
-Japan: Also might sort well...maybe? US military in Osaka might be able to 'take over' as far as occupation goes, at least temporarily, and continue with trials and the like for Japanese war criminals--and shit like the Unit 731 pardons can be avoided. On the other hand...Japanese occupation took more than 300,000 soldiers and a quick internet check says modern US deployment amounts to only ~50,000. That's quite a difference, but maybe modern technology can make up for it?
-Middle East: 'Shitshow' comes to mind? Little Soviet stuff to be concerned with, but the US has penny-packet deployments in a half-dozen ME states, and that'll be a mess most likely and...I just now think of the matter of war stock being held in other countries. If that goes back in time as well because it's technically AMerican, the Saudis, Norway, and Israel at least (I don't know where else there are similar storage sites) are going to find themselves awash in suddenly-existing bunkers that are packed with modern military equipment. That's a wrinkle for folks to consider.
-South America: This one seems like it's going to need a mass humanitarian/aid/development package? US draws on a lot of materials in SA for stuff--bauxite and Bolivia being the stereotypical example that comes to mind--and letting things slide with preexisting caudillos or installing new ones isn't going to attract much popular support in the US. Seems like there'd be a public outcry for some actual good-faith aid and assistance in the region rather than the meddling-about the US engaged in (to put things lightly) through the period.
