There are various theories about what caused the change in Kim's behavior. China put him in his place? The new president of South Korea is willing to engage with him? Now that he has nuclear capability, he can pretend to disarm? But it's all guesswork. We don't know what motivates him, because he's the absolute ruler of an intensely secretive state; we know very little about him. Look at his Wikipedia article: we don't even know for sure when he was born. How could we know how he thinks?
Trump supporters are already crediting him for achieving peace in the Korean Peninsula and saying that he should get a Nobel Peace Prize. Such celebrations are premature. There were inter-Korean summits before. In 2000, Kim Jonh-il
met and shook hands with South Korean president Kim Dae-jung. They
signed a declaration about peace and collaboration and formally ending the Korean War. Kim Dae-jung later won the Nobel Peace Prize in part for his work for reconciliation with North Korea. Didn't exactly work out.
In 2007, there was another inter-Korean summit. Kim Jong-il
met and shook hands with South Korean president Roh Moo-hyun. Yet again they talked about formally ending the Korean War. North Korea agreed to disable their nuclear facilities by the end of the year "in a move that the Bush administration hailed as a diplomatic victory that could serve as a model for how to deal with Iran" as the New York Times wrote at the time. And nothing came of it.
This time, things are a different though; the North Korean leader went to South which has never happened before, and there's a planned meeting between the US president and the North Korean leader, also never happened before. But still, declarations are easy. North Korean leaders don't have to fear that their people will call them to account if they don't keep their promises.
But I have to admit, painful as it is, that part of me wants this to fail. Rationally, I know that success would be great. But the idea that Trump is responsible for this causes me intense cognitive dissonance. It's not just that I hate him. I don't want to believe that the way he behaves - acting like a deranged goon, making threats on Twitter, giving Kim a schoolyard nickname - is a successful approach to international diplomacy. I want to believe that maturity, self-restraint, expertise and careful language are necessary. On an emotional level, this is more important to me than peace in Korea. And it's just terrible that I feel like that. It's pathetic.
As far as we can discern, the sole purpose of human existence is to kindle a light in the darkness of mere being.
--Carl Jung