As you probably know, North Korea recently had a nuclear test, prompting UN sanctions (which South Korea signed on to), which in turn saw North Korea ending its armistice agreements with the South, cutting communications, and issuing threats against its neighbours.
The US has unfortunately been pushing Iran around on nuclear technologies, probably because the Likudniks presently in office in Israel have been pushing for war, and AIPAC (and to a lesser extent J-Street) are powerful lobby groups in DC supporting an unfortunately pro-Israel (and usually pro-Likud) US foreign policy. I've never been worried about Iran, and would be entirely comfortable with them having nuclear power and even nuclear weapons. North Korea, like Libya was under Qaddafi, is not the same; the degree of despotism and detachment from reality in those nations is much more severe (as is/was visible in their state media), they're a constant threat to regional security, they're police states with cults of personality, and they spend far too much of their GDP on their military and make it culturally prominent. North Korea is also dependent on food aid, but continues its excessive levels of military spending with its resources.
North Korea has long worried China, and China's hardly been a principled nation concerned with broad human public goods. Like the US has often been in practice (but not so much in rhetoric in recent decades), China will do business with anyone if there's coin involved, placing reputation a distant second, happily dealing with brutal dictators in Africa so long as such dealings increase China's presence and prominence. NK's behaviour has worried China because fear and war are bad for business.
I hope that China is prepared to push a rapid, forcible regime change in North Korea should NK aggression continue. I don't think, given how NK society works, that we can expect a significant change to their political culture until and unless they get a monarch that decides to liberalise. I'm not sure, given how the country is run, we can trust the nation not to initiate violence in the meantime. I don't think anyone but China could push North Korea over rapidly enough to prevent potential disaster from their missiles, and I believe China has the capability and the interest in such a regime change. I believe such a regime change would also be very low risk in the sense of not being likely to make life worse for North Koreans. A post-transition plan would be reasonably obvious; joint Chinese-SouthKorean-andpossiblyRussian administration for some decades until society normalises.