If you were a british pilot stationed at the dover cliffs during WW2, would you continue to sip tea, read the dailies when War HQ Intelligence tells you that a german V2 had just lifted off and on its way across the French Coast, or would you scramble and take flight, search the skies with the intention of locating that V2 to shoot it down before it bombs more of London, more so when Germany had declared war on England?
The brit pilots did the latter, as ANYTHING that flies out of german controlled land is considered an ACT OF WAR.
Not only did they try to shoot down those missiles, they and the american bomber units even flew into german occupied terrorities and even into Germany itself to bomb the crap out the aggressors.
America had never been interested in conquest. S.Kore desires reunification, but knows it cannot do so alone, nor is there a need to. Our world's peace and evolution is dependent on mutual economic cooperation for progress. China knows that too, and they share the world's concern over nuclear proliferation.
S.Korea is not desirous of nukes, nor is Japan, for they know that if they live by the nuke, they may one day die by the nuke. They are fine with the status quo, as economic progress is what they rather want, unless pushed into nukes such as what Fatboy is doing to them right now. And thus China's anger at NK, for China have no wish to have mass produced nukes from asia pointing at them.
So long as Asian states do not seek for nukes, but focus on economic progress as it had done for decades, China will stand aside, and may even weld its hand against any that seeks to want nukes, inclulding even its own allies - NK and Cambodia. China too needs economic progress to stay in power, or its hungry masses will rise up. The past 3 decades had successfully shown what China can and will be if it pursues economic strengths sharing our world in peace instead of following the failed Maoist of domination and stupid military might.
In any case, the moment red lines had been crossed, Fatboy kim will be in deep sh*t, and no law or victim card can save him, for 7 billion of humans are not fools, and do know the mitigating factors for nations to defend themselves against agreessors that Fatboy Kim's regime of decades had proven themself to be.
Mankind will not be bullied, no matter how many ganster friends Fatboy Kim has, because the day we cower in fear of them, is the day that proves our cowardice to protect our own fellow citizens against bullies, and have no right to even be a sovereign state.