Andrei Lankov, professor at Kookmin University, South Korea writes in the New York Times:-
North Korean leaders are sending a message. For the last two years, both Washington and Seoul have tried to ignore them, so now they use both artillery and centrifuges to say: “We are here, we are dangerous, and we cannot be ignored. We can make a lot of trouble, but also we behave reasonably if rewarded generously enough.” ….So long as the Kim family stays in power — and it could be around for a long time — North Korea will remain a problem with no diplomatic solution. It survives by making trouble, since it has to make trouble just to stay afloat.