Pyongyang is like the yappy little terrier down the street that comes out barking up a storm whenever you walk your shepherd by.  The mottto of "the best defence is a good offence" is very applicable in this case.
In many ways, the real leader of N Korea is the military, and they are for all intents and purposes still stuck in a Cold War/1950s mindset of paranoia.  There is no question that Kim Jong-un is as crazy as an outhouse rat, but, there is method to his madness.  He wants to keep power and the only way to do that is to prove to the military that he will stand up to the evil imperialists.  So, when we ramp up our rhetoric, you can bet that they certainly will.  Just like the yappy mutt down the street.
It is very unlikely that N Korea, despite the rhetoric, would ever start a war.  They would get eradicated.  Period.  But it would be a messy eradication for all concerned.
It's called diplomacy for a reason, and in this case, diplomacy is a far better option than the alternative.