Let me say that if Donald Trump is able to finalize a serious agreement in Korea that brings an official end to the war there as well as establishing some kind of peaceful settlement in general that leads to some sort of mutually acceptable arrangement between the two Koreas that maintains a peaceful situation for some reasonably lengthy time into the future, pretty much irrespective of the exact details, I shall applaud. I shall not even hold my nose if somehow he gets the Nobel Peace Prize for it, as advocated by ROK president Moon Jae-in, although it is the latter who is the far more deserving recipient. But maybe such an award would have several recipients for it, if it happens. A few observations in any case.
I suspect that the importance of Trump's loud sabre-rattling has been exaggerated, certainly in the US media, but I shall not say it has played no part. But certainly important has been the substantial heightening of economic sanctions that came in over the past year as DPRK president Kim Jong-un carried out a series of major nuclear weapons and missile tests, culminating with a claim of testing an H-bomb and obtaining a sufficient nuclear weapons stache for deterrent purposes. Most important in this was China finally enforcing much stricter economic sanctions on the DPRK, either out of trying to please Trump, or out of increasing annoyance with Kim, or more likely a combination of both. As it is, Kim visited Beijing (by train) just before announcing his willingness to visit the ROK, and in fact China has been easing the economic sanctions since then. Without doubt this played a huge role, if not all that widely acknowledged, and even as all along pretty much everybody said that DPRK would not act until China put the economic squeeze on, and it finally did.
The other major player, probably the most important one, has been ROK president Moon Jae-in, who has managed cleverly to keep not only Trump but most US commentators and media from realizing that he has successfully manipulated Trump into supporting his diplomatic opening. It must be remembered that last year when Moon first came to office (and he would have come to office if Hillary was prez), he proposed and advocated a diplomatic opening. This was largely sneered at by Trump and those around him, with Abe of Japan and Xi of China receiving praise from Trump, who rather grudgingly acknowledged Moon as an "ally." It was Moon who pulled off getting Kim to attend the Winter Olympics in ROK, even though he allowed Trump to take credit for it. He has been repeatedly giving credit to Trump for everything since, even though most of it has been his own doing. But he has managed to get Trump on board, and indeed he needs Trump to finalize parts of this, including especially formally ending the Korean War from two thirds of a century ago.
I hope it all turns out well (and I remind any who do not remember, that I have posted here previously on how the hawkish policy by W. Bush after he came into office in 2001 pushed the DPRK to leave the NNPT and acquire the nuclear weapons it has, something not irrelevant to Trump's current approach to the Iranian nuclear deal).