solarz
Brigadier
It's pretty easy to ensure that an administration friendly to China would be in control of a united Korea, after all, the US has dozens of such countries scattered around the world including NATO and the current SK administration. You need a common adversary, that's all. For the US and NATO, their common adversary is Russia and for the US and her Asian-Pacific allies, it's China.
If China was to convince a new united Korean administration to be friendly, then their common adversary would be a re-militarised Japan. It's impossible for Japan to not re-militarise if a second Korean war broke out, and once they do, China and Korea are going to be fuming. It's a damned-if-you-do, damned-if-you-don't situation for Japan. On one hand, they cannot possibly take no action in a second Korean war, and once they do, it will virtually guarantee that the new Korean administration will choose to seek cooperation with China.
Yes, you're right, the key is a common adversary. Thanks for pointing that out.
It sounds like a re-militarized Japan might actually prove to be a good thing for China in the end.