First, NK was never a serious threat to anyone except its own citizens.
I've been saying this for years. He has a very nice life for himself in North Korea, he knows that all ends very quickly if he actually nukes anyone. Personally, I'd be more worried about the militant Islamists who have influence in Pakistan.

Really though I don't think NK and SK meeting is all that big a deal
It's a massive deal though. Maybe it has major role in your life, but this has been ongoing for a very long time and it causes problems between USA and China, as well as causing untold misery across the Korean peninsula.

Second, while I'm happy if NK and SK stop arguing I don't think it is a monumental world event. Get India and Pakistan (who both have nukes, but which doesn't seem to bother the US) to stop arguing or Israel (with nukes) and 10 of its closest neighbors to stop arguing and you've really accomplished something.
It's on a par with India and Pakistan, and the Israel situation is probably the only global security problem that is indeed more serious.

That the media plays up NK/SK as an important place in terms of world peace just shows how little is going on in the other danger zones.
More like how much they don't want to you know.

Third, even if this goes through to a happy ending, there's no reason to think the US had a lot to do with it. China is by far NK's biggest trading partner, and if anyone put the screws on Kim it was them.
Why do you suppose China suddenly starting twisting the knife?