He can't actually do anything serious, because he understands that this instance it will be over. His power is only in menacing the world, like the dog barking on a leash. If he crosses the line he loses it. The world had to start pressuring North Korea long time ago. It must be an effort of all countries in the UN to make North Korea abandon its political regime and reunite South Korea. There should be all sorts of blockades, but also food humanitarian help. There should be programs helping people leave NK, amnesty programs for all officials who give up etc. That sort of large scale global pressure, and it had to start 20 years ago, when they only started nuclear development. But Russia and mostly China aren't helping and make all the effort futile, instead using NK in political games. And now we have horrible gang of people with nuclear weapons, ready to terrorize the world.