> Let's remember that several western countries do not want a united Korea either.
Name one.
> North Korea has the biggest standing army of the world.
No, it doesn't. The US, China and (India, IIRC) all have larger standing armies.
> Other asians are still very wary of ethnic Koreans, in Japan for example it is known that while there are several non-japanese citizens, ethinic Koreans rarely get citizenship.
This is a poor and complex example. Several quite Japan-specific cultural issues are at play here. It's also not as welcoming to non-Korean foreigners as you seem to imply.
> The united Koreas... maybe they will start another crazy war and attempt to conquer Japan or China.
This is ridiculous.
> ...every time one Korea is losing advantage in the stalemate, that Korea gets some sort of clandestine or official help, in a way to force the stalemate to continue, and the biggest army of the world divided in half and turned into itself.
Aside from the factual inaccuracies ("biggest army of the world"), this feels like a half cooked conspiracy theory. Do you have any evidence whatsoever?