Mmm.. I see what you are saying, but do the numbers really support this?
First, what people are you considering Asian? The continent includes Russia, China, Mongolia, India, Vietnam, Korea, Laos, etc... That's a large swath of humanity.
All of that. Yeah.
The thing is, I think the death toll is much higher than the 600 million. That number was referring to causalities from WW3. The next... almost century of that region being a post-apocalyptic wasteland would have resulted in a huge number of deaths.
I do think some places fared better than others. Japan and Korea may have gotten through a bit better. I'm not saying like, the entirety of Asia got glassed and wiped off the map... just that it was hit significantly harder.
From "The Royale"
WORF: Commander.
DATA: Is this significant, sir?
(It's a spacesuit on a hangar)
RIKER: American.
DATA: Fifty two stars sir. Places it between 2033 and 2079 AD. It correlates with the debris we found. Colonel S. Richey. Rest in peace, Colonel.
There were 52 states in the United States of America in 2063
Yes... but... the United States would never have recognized the ECON as a nation, so if the ECON breaks off in say... 2040, the US isn't going to change it's flag because some of its states are in revolt against it nor it would stop consider those states as longer being a part of the United States.
It could even still track, as the ECON apparently still existed as of 2063. There seems to not have been open warfare in awhile, "After all these years?" but that doesn't mean it ceased to exist. It may have taken some time after first contact for the US to fully reunite and reabsorb the Eastern Coalition, which might make sense why the flag changed again in 2079.
This isn't an ironclad headcanon by any means, more of a general pondering. It PROBABLY makes more sense that the ECON was an Asian faction in the war, but I think being a part of the SACW could be interesting and could provide a tie-in for Colonel Green.
Part of what triggered the idea is Picard making sure to quickly make sure he identified that was he was not a member of the ECON. That line makes it feel like that's more a domestic enemy who you very well might encounter randomly, rather than a distant foreign enemy.