They're all bark and no bite.
While that's largely true.
There is a problem.
The problem comes from the unknown.
We do not fully understand how DPRK is governed day to day.
How much power does Kim Jong Un really have?
Is he just a figurehead that a Junta uses for propaganda?
More realistically Kim Jong Un is under increasing pressure, from China and I theorize that there is intense internal power struggles in DPRK that we do not understand, conservative elements within the DPRK Elite were not happy such a young man became leader and with more western thinking, the authorities have actually, slowly but surely increased private transaction markets in an attempt to deal with the governments lack of ability to repair their own distribution system completely destroyed in the early 90's.
I theorize the way KJU attempts to offset these internal power struggles against him is two fold.
We have seen purges and we have seen acts of aggression, his however were more dangerous than his fathers sabre rattling.
Kim Jong Il was at least a practical man and despite some of the more macabre acts of kidnapping and violence in his early days, did things specifically to bring others to the table and get some form of concession in return for standing down.
Kim Jong Un appears far more aggressive for others reasons and because we don't understand them, if KJU was ever pushed in a corner, more specifically by the internal power struggles within DPRK and he felt so threatened for his life that the only way out was an act of unbridled aggression that pushed us beyond the brink... Then god help the Korean People, North and South.