China would be the more interesting place being the other major superpower. With a huge American invasion ongoing when it all went to crap.
You could even have a bit of Americana still going on and familiar tech like the T-51 Power Armours while basing the game in China. Surviving remnant US forces would have set up shop and rebuilt their own slice of America wherever they are. Just like how the Shi set up shop in San Fran and recreated their own Chinatown. Might be a stretch but I think it's possible to keep the 50's Americana to some degree with enough creativity.
You could even have a bit of Americana still going on and familiar tech like the T-51 Power Armours while basing the game in China. Surviving remnant US forces would have set up shop and rebuilt their own slice of America wherever they are. Just like how the Shi set up shop in San Fran and recreated their own Chinatown. Might be a stretch but I think it's possible to keep the 50's Americana to some degree with enough creativity.