It should be noted that historically, Korea has always been subservient to China.  This goes back hundreds of years.  China has received more from Korea, and Korea has always depended on China to help and protect them.  You cannot break this tie between those two countries.  If the US would take the preemptive strike approach, China will intervene on behalf of NK.  If NK/KJU makes that first and fatal move, it will be NK/KJU problem to resolve.  Best bet is to also provoke China by its' interference of militarily supporting NK/KJU.  Take 'em all on.  This is good strategy, since China doesn't really want to get into a real shooting match with the USA.  They are now too fond of MONEY!!!!