My brother told me a different story, though none of this is confirmed, but rather rumors.

Some people are saying that Kim is being stopped by none other than the his sister, the queen of gulags herself. Unlike Kim, she is an actual politician, and it is said that she fears repercussions of Kim's aggressive attitude and hot-headed actions, and that would put quite a hamper on her plans to keep things under control if the US was to retaliate strongly. That would go to explain Kim's odd and sudden change of mind at the Trump meeting and opting for peace after testing like 3 bombs not long ago. He was very obviously ready to go to war, but NK's government is not one single united mind; Kim acts on his own volition, and truly, he is just a spoiled child who inherited a lot of power.

This would actually be quite an interesting story for a documentary if it was true.

I think it's most likely China. They were the reason they didn't lose the Korean war, and kept them alive to keep a buffer zone with US backed South Korea. Now, even them are tired of NK and they have become more trouble than worth.

NK did an 180° when China announced they wouldn't back them if they caused a war. And that's just what is public, I think that privately China and NK relations are even more tense.