Now, North Korean leader Kim Jong-un is making an unprecedented trip south of the border to meet with South Korean President Moon Jae-in. And Kim's nuclear arsenal is only one item on the agenda.
Catherine Killough studies North Korea's nuclear and missile programs for the Ploughshares Fund.
During an interview with Newsy, Killough said, "You don't have to be a Korea expert to know that this is one of the most intense, unprecedented years of tension between North Korea and the U.S."
"I think there will be at least three different things that we'll see in this joint declaration," Killough said.
"First is a commitment to improve inter-Korean relations. And that may come in the form of reuniting families, talking about economic cooperation and ending military hostilities," she said.
"Another proposal that's been floating around from South Korea's spy chief is a formal end to the Korean War," she said.
So, just as a reminder, the Korean War never formally ended. An armistice signed in 1953 halted the actual fighting, but the two countries are still technically at war. The Demilitarized Zone separating the two Koreas is one of the most heavily fortified borders in the world.
"This is an issue that has not moved forward in decades. And peace is a process," Killough said. "Peace is as difficult if not more difficult than denuclearization. So to have two leaders actually willing to talk about it, that would be a really big deal."
And then, of course, there are the nukes.
Killough told Newsy, "The third really important objective is, for the South Koreans, is to get Kim Jong-un on paper, on record, saying he's willing to talk about denuclearization."
"If we go back to 2013, we can see that North Korea has been waiting for this moment. In 2013, Kim Jong-un adopted this new byungjin policy. It's a parallel track of development: nuclear program and the economy. In 2018, New Year's address, he said, 'We've completed our nuclear force,' so he checked that box off. What we may be witnessing now is this pivot to the economy," she said.
"It's also important to test how serious Kim Jong-un may be about denuclearization. And that will inform talking points and negotiations on the U.S. side," Killough said.
President Donald Trump is expected to meet with Kim sometime in the near future. Whatever agreement Moon and Kim reach at this summit could set up how Trump's meeting with Kim will go.
"I think President Trump is serious about getting a victory out of this," Killough said. "If he can come out as the guy who solved Korea, that would be big."