In reality, if we're really honest about things, 'Russians' stop being Russians East from the Urals. Russians are white Europeans. Everything East of the Urals is just conquered land, conquered by some barbaric czars. Not that it should be returned or what not, but it's a fact that when push comes to shove, Russia will ally with the West, and not with the East.
About North Korea, never mind them. They need a controlled 'collapse', and that will only happen if and when US troops have left the South. China would and should never allow US troops stationed on it's own borders..
The only disputed China and Japan have over territory are some uninhabited islands. In the greater scheme of things, with trillions of dollars of mutual trade and investments, those tiny little island disputes can easily be solved by compromise. Heck, you'll see the bigger disputes, like Kashmir, being solved because of those reasons, so never mind uninhabited islands. It just takes time. But in the end, the interests of Japan, China and Korea are a lot closer than those of far away countries.
First of all, Not really much of a point saying what land "
SHOULD" belong to Russia, if you claim so, how about Russia never existed? How about What if Germany or France conquered Russia by winning Stalingrad and Moscow or What if Napoleon won the Battle of Waterloo.
You ask a what if question about the future, and the future is based on actual history now, hence what you think what Russia belong
DOES NOT MATTER, what matter is that Russia control East of Ural NOW. And if you have to go and ask what if there are East Asian union, then you need to factor in Russia with the threat level as of current, otherwise if you want to go with the "Alternative History" lane, then your question is nothing more than a fictional story,
Second point is, you cannot "Control Collapse" a nuclear power, you can do it before in the 1950 by NOT intervening the Korea War and let the US and UN force conquer North Korea, and unify it. Then there will not be a reason for US to station troop in Korea and in some sense, even japan, but the problem is, you intervened, that's in hind sight is the dumbest thing you can do. As China now created a buffer that unstable and missed the chance to capture Taiwan.
Thirdly, Economy is not
EVERYTHING and you are seriously underestimate Japan. Even if Chinese GDP are 6 times of Japanese own, Japan simply won't fold and enter into a Union with China, US bombed Japan to shit during WW2, that's Zero Productivities for those who care to think about, and they did not enter a Union with US instead they stated independent. And even in historic term, refused to denounce the emperor and accept certain demand to "bend over" to the US, who actually asked for an unconditional surrender. They have more national pride than any one else, including the US and China
You are, as with other Chinese member here, over-estimated the Economic Aspect, you expect if you invest in some country then that country will fall into line, but you know what happened in reality? in Real history? Those Country will simply say thank you then took your money and ran. Again, as I mentioned many time in this forum, it had happened to the US in the 50s (Cuba), 60s (Laos), 70s (Afghanistan), 80s (Iran) and 90s (Iraq), what, why and how would you think they will not happen to China??
Business is Business, Political affiliation is another Question. It is dangerous to think investment and trade can forge long lasting relation. What if someone offer a bigger pie to that country? Would you think they will not switch side?
Now, this is the Reality