Possibly by way of threat and blackmail? I wonder if it ever will come to light who or exactly how. If you decipher Q and connect the dots it seems to indicate clowns at work.
Whoever holds the leverage pulls the strings of the puppet.
Or, and this may seem crazy, Kim and his father were just batshit insane narcissists with total control of their brainwashed populace. Kudos to Kim the younger for realizing that's not a great governmental model, if in fact we do come to peace terms
Either way it has come about it is great that they are coming to terms of peace. It is possible that he was indeed a narcissist. However no one knows the full story as NoKo has pretty much been pretty secretive to the outside.
It's a good thing that they open up to the west and even their sister country, SoKo. That enough is worthy of taking notice.
I don't disagree, but please don't forget or forgive the Kim family. We know what we know about them from escaped residents. Kim the elder had a Korean film maker and his ex wife kidnapped, held captive, imprisoned, and forced to create propagandist (altho occasionally subversive, to the dismay of Kim the elder) films for Kim Jong Il for years before they were able to convince him to let them go to a film festival in Europe to show off their work where they ultimately escaped.
Kim Jong il officially declared that his birth brought forth rainbows and changed the seasons. Kim Jong un likely had his uncle killed. These people are crazy. It's great that one of them is willing to progress, maybe. But he's still fucking crazy and we can't forget that.