>>52079102pokemon is a post apocalyptic series.
pokemon came to a earth that was originally very like ours and as you'd expect guns happened.
and if you remember what guzzlord was before nukes you can guess how that ended.
by the time of the games we see poke-earth has seen countless apocalypses and massive global population shifts before reaching some resemblance of stability.
a pokespain being built on the ruins of a new China is not really that weird for the pokemon world.
kanto is more or less the only region humans have occupied since pre-mon era and many are likely only recently colonized if the quick construction in unova is anything to go by and sinnoh is explicitly stated to be an older region with only about a hundred years of history.
