They're pissed off at new UN sanctions imposed on them over their nuclear program. Theyre also pissed at US for beefing up their missile defense shield aimed at them saying N Korean missiles can hit Hawaii. They're always pissed at something. There has never been a peace treaty to end the last Korean War, just an armistice to stop the fighting.

The only thing that has kept them from attacking S Korea are all the nukes we have pointed at them in S Korea. The last time they attacked they lost their entire army and it took a million man army from China to save them.

It will be even worse this time.