Because we've spent the last thirty years fooling with Agreed Frameworks and Six-Way Talks and giving provocations a pass

North Korea's rocket and artillery forces are on their highest alert level ever.  The announcement of it includes talk of the US mainland.

At least we're finally trying to muster some degree of actual seriousness about the spike in NorKor bellicosity, signing a new treaty with South Korea that unprecedentedly specifies the role the US would play in an attack on the South.

Ed Morrissey at Hot Air:

In other words, no one’s going to assume that a conflict erupting on the border or in the Yellow Sea is just an accident any longer.  The US and South Korea are both warning Pyongyang that it will react as though the DPRK intends to open a wider war in those circumstances, striking back not with corresponding force but with overwhelming force. Over the last several decades there have been a number of these hot flashes in a cold war, but most of them have remained single-incident flashes that ended quickly and without engaging wider forces.  Thanks to the rhetoric and the actions of Kim regime, those safety valves now appear to be off the table.

The next time there's  a downed-airliner / torpedoed sub / rocketed fishing village-type incident, it will be impossible to respond with the usual "this-is-unhelpful" rhetoric.

And there will be one.