Yeah, one thing I'm honestly not happy about in this show is just how much the make-up of the world is glossed over; it's a mistake, because a lot of political maneuvering,
especially American and Japanese may not make sense if you don't know the stuff.
As usual though, Muv Luv wiki can help.
Basically, Japan and it's Co-Prosperity Sphere (called Far Eastern Alliance because of all the media taboo) surrendered to Americans, and was largely allowed to remain intact. Shogunate also continued to exist to present day, though towards 2000s, the Shogun has increasingly smaller control over his/her government in same manner as the Emperor.
Nukes were dropped on Berlin instead.
European Union was created earlier due to various hijinks between NATO members and the U.S, and China was the first nation to go when BETAs invaded Earth. They were effectively wiped out, though a reminder of their military is still trying to hold out (Taiwan is also untouched, mainly due to U.S presence) and they play some role in Total Eclipse.
America itself is also the pinnacle of logical, but incredibly dickish trolling. They basically pull "Screw This, We're out of Here" after Fall of Kyoto, essentially abandoning Japan when it needed their help the most and effectively rendering the whole defense treaty thing null. They also dropped most of their nuclear arsenal on Canada. To kill a BETA Hive, mind you, but they didn't warn either Canadian people or Canadian government. Suffice to say, Canada really hates the U.S (and in another Alternative Timeline, they actually go to war with the States together with France...and are apparently winning.)
U.S is also prone to making really fucking stupid strategic decisions like adopting F-22A Raptor for its next-gen TSF, which is worse in Anti-BETA combat then its contender, the YF-23 Black Widow II, and whose stealth capacity clearly indicates American willingness to engage other human forces just as entire species is about to get exterminated. The American back-up plan also revolves on using massive arsenal of completely unknown superweapons - and not even their creators know how they really work.
On the other hand, most of reminder of Mankind lives within United States (including an absolutely massive amount of refugees, which make current migrant problem look fairly small-time), so U.S victory is essentially one for mankind.
Also, Japan itself is fairly full of assholes themselves, they just don't have the power to pull of the things America does.
And there's the whole deal about Soviets being granted leased territory in Alaska.
And yeah, TSF designs are awesome. The SU-47E Berkut in particular is probably the most bad-ass mecha design I've seen in my life.