Under what justification would they attack NK. Methinks China might have a wee problem with that. But attacking NK would just be insane. The guy may be crazy but he is crazy like a fox. He is all bluff and bluster. He also has a huge army and if you do attack him he won't hesitate to hit back and also maybe hit Seoul as well. And then there is China. China will not tolerate it. And then lo you  are also at war with China and WW3 is on with nuclear weapons.