Does anyone realize that if North Korea launched a nuclear tipped ICBM and successfully struck the US and we were going to retaliate in a massive manner, every country in the region would demand that we not do so, as the result would be massive radioactive contamination in the region.  China would threaten to start WW III over this and even allies would insist we just can't follow through with this or they could even become our adversaries.  The only option for the US is a conventional invasion, which would cause North Korea to attack the South and bring them into the war too.  Also, China would not tolerate an invasion resulting in their border now occupied by an opponent.  So, China would be forced to do the invasion themselves to preclude this and topple Kim and his military, especially if he has already lobbed a nuke at South Korea too and started the radioactive contamination.