I'm under the impression that you can now fire at an ally of the USA if you're an ally of China. YOU need THEIR bucks. Else it would be south Korea that would be showing its muscles.
I wonder how china will react, but nobody will do ANYTHING without their consent.
I'm not so sure, which is why everyone is kinda on edge now. Russia is seriously pissed at N. Korea (they don't want a hot war on their border), and the South Korean leadership is far less conciliatory than the last few administrations. Lee Myung Bak might actually take this to a whole 'nother level by launching a retaliatory strike beyond the in-kind artillery response, maybe an airstrike on DPRK artillery positions. But if he does, this thing could quickly turn into a serious clusterf**k. North Korea could turn half of Seoul into rubble in hours just with conventional artillery. Doing so would inevitably mean firing on US troops (which is really their whole point -- not to fight off the North Koreans, but to be targets to give us a
casus belli), which would trigger US intervention. If the US got seriously involved, I imagine the Japanese would sign on for a piece of the action, although that's not a certainty.
It's at that point that Beijing would have to examine the situation and figure out what's in their best interests. My gut feeling is that they would cut off the potential for a hot war on the peninsula by taking out North Korea themselves and making it a protectorate/client state/puppet state/etc. before we even had time to get our carriers in position. And I don't think too many people would protest a Chinese takeover at this point. Saves a lot of cost and grief by the US, Japan, etc. Beijing doesn't particularly want to have to administer North Korea because it's more cost than it's worth, but they want chaos even less.
War on the border is chaos. Millions of refugees fleeing into Dongbei is chaos.