North Korea doesn't have a viable nuclear weapon yet. To be useful it has to be small enough to be delivered on a missile. That is one of the challenges they are making progress with. The other is developing a missile (ICBM) capable of delivering a nuclear missile to a distant target. They are making rapid progress with that. They could already hit some of the neighbours and it won't be long before they could hit the USA.
The history of it is that Russia gave them nuclear reactor technology that can be used to produce weapons-grade material. Pakistan sold them missile technology.
Something has to be done. Kim Jong-un is unhinged. The whole country is one big personality cult. He is surrounded by yes-men and anybody who disagrees with him is publicly executed. Hatred for the west - USA in particular - is the central tenet of the cult.
China was the "honest broker" but there are reports that the Chinese ambassador was refused an audience with his NK counterpart this week.
NK cannot be allowed to possess a viable nuclear weapon. They danger that they will use it preemptively is too great.
Nobody seems to know how to prevent it though. It is estimated that a conventional military intervention against NK could cost a million lives. There is no easy answer. I also grew up during the Cold War. We have seen all manner of crises come and go. This one actually has potential to be different.