Well speaking as an American I would love if some of our allies would join in to help us fight off oppression and gain back our freedom.

But if I were to speak on a international view, only reason i could see to help America is for the economic support it provides. However, I wouldn't go in to help stop oppression because America wasn't there from the beginning when Nazi Germany took over Europe. Nor where they ever there when atrocities were happening in Africa, South America, Asia, etc (although we did help contribute to it). Nor with their policies of arrogance and "policing" the world would I think it necessary to help them out.

Really America has obtained a bad reputation of having a superiority complex to other countries and its hard to imagine I'd want to help that which probably wouldn't help us given the scenario. Nor would I want to make an enemy of China especially if they are good enough to beat America. However, the idealist in me would probably overrule as no one deserves to suffer under a totalitarian government. Even though America wouldn't do the same for others, if I were a non-citizen, I would feel obligated to do the right thing. Although peaceful negotiations first before all out attack. A wise man once said, "You can't obtain peace through war. Only through understanding"- Einstein. Maybe if America knew that from the beginning we would have been better off. Maybe the world would have been better off.

With Nato support.  Since this is "Should your country help after the US was invaded" i'm talking about after an invasion.

I'd guess by the time they invaded they'd have carriers.   I mean, as you said it'd probably take 7-10 million troops.  Currently the Chinese army is under 5 million... and mostley domestic to my knowlede.  Meaning they'd probably need to come up with 5-10 million more troops.

I agree there... they could get some ok technology and armarments attacking Russia as well.

The rest... i'm not so sure.  Would the middle class be effected much by the war?  You look at the US... and we haven't been hit at all by the two wars we've been in.

Its never been proven that Russia's desire was to take over Europe. Sure, Imo, they wanted to expand a bit but I still think future safety was their main motive and understandable motive.

Being an American, I know we do a lot of things wrong. It isn't the people though, it's our government that feels the need to get involved with everything. That being said, we have helped out so many people in our lifetimes, with getting involved in wars, restoring other country's peace, and helping people recover from natural disasters, I would only hope when we have a time in need people would help us.

I should have tempered the "anywhere in the world" statement. The US hasn't been effected that much because the war is so distant. But an invasion of Mongolia and Kazakstan would definitely bring the country in to direct conflict with Russia. The U.S. never had to worry about the Republican guard rolling it's tanks through their neighborhood. Two major military powers that boarder each other would be monstrous for all involved.

Of course, there'd be the hope that both countries would want to avoid that and would merely cut up the stans and Mongolia to their liking like Korea. Infact, if there's another major war in our lifetime, I'm farily certain it will end up with the Stans mostly occupied.

Isn't the Chinese middle class pretty much located only in the south eastern area of China?

Yeah, but they're still well within the range of the Russian airforce, Navy and missiles. Also they'd still see much more pronounced impacts of the war such as a flood of refugees and a lot of economic upheaval. And, like I said, there are many parts of China where the people aren't too happy with China. Having the country's army occupied with something like that would really be their opportunity to push for independence.