SEOUL, South Korea (AP) — It may lack the punch of President Donald Trump's vow to unleash "fire and fury" and North Korean leader Kim Jong Un's "nuclear button" boasts, but the stakes will be high on Friday when Kim and South Korean President Moon Jae-in sit down on the southern side of the no man's land that forms the world's most heavily armed border.

Kim may never abandon the nuclear weapons that he claims are all that stand between him and annihilation, but if the Koreas and the United States are going to begin stepping away from what, until a few months ago, looked like a real possibility of nuclear war, then Kim and Moon must lay the foundation with a successful summit of their own. The fate of a planned Trump-Kim meeting, possibly next month, is also linked to what happens Friday.

The rival Koreas' long, bitter history will provide skeptics with ample fodder to doubt that any real deal can be reached. Since a tenuous Korean War cease-fire took hold in 1953, every major initiative to settle the world's last remaining Cold War standoff has eventually stalled.

So what's the goal? What would "success" look like?

Some sort of progress on nuclear weapons, even it falls short of a "breakthrough," headlines the list, but there's also, from the North Korean perspective, the "problem" of nearly 30,000 heavily armed U.S. troops stationed in the South, and the failure to agree on a peace treaty formally ending the war, a situation that the North routinely says creates the hostility that makes its own nuclear weapons necessary.

Here is a look at how we got here, what the two sides want, and the chances that a real deal can be achieved:

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FROM THREATS TO TALKS

Moon, a liberal who cut his political teeth as a lead architect of a previous government's "sunshine policy" of engagement with North Korea, came into office last year hoping for better ties with the North. Instead, one of the most heated North Korean weapons-testing outbursts in recent memory forced him to follow Washington in ramping up pressure on the North.

Then, in January, Kim began a charm offensive by declaring that North Korea had "achieved the goal of completing our state nuclear force" and opening the door to diplomacy. Analysts believe that North Korean technicians still have some work to do to make this a fact, but the important thing, from Moon's viewpoint, was the shift to engagement.

The Olympic Games in the South Korean mountain resort of Pyeongchang in February provided the perfect backdrop for that diplomacy to flourish. Kim sent his sister to Pyeongchang with a summit invitation for Moon, and the two Koreas marched together at the opening ceremony and formed a single women's hockey team.

During a visit by a high-level South Korean official to North Korea, Kim reportedly announced that he wouldn't need nuclear weapons if his government's security could be guaranteed and external threats were removed. He also reportedly offered to meet with Trump and stop weapons testing as the diplomacy plays out.

After learning from South Korea of Kim's offer to meet, Trump shocked the world by accepting.

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WHERE'S THIS HAPPENING?

The short answer: Someplace where Kim won't feel entirely comfortable.

Succeed or fail, there will be some indelible images from this summit as the North Korean leader ventures out of his stronghold in Pyongyang and onto what is technically South Korean soil — the first of the three Kim family rulers to cross the border since the Korean War.

To get to the South Korean-controlled Peace House on the southern side of the Demilitarized Zone, in the border village of Panmunjom, Kim will have to cross over the border, possibly on foot, near the spot where a defecting North Korean soldier recently fled south in a hail of bullets fired by his former comrades.

Panmunjom is about 50 kilometers (30 miles) north of Seoul and the site of the signing of the armistice that ended fighting in 1953 — but not the war, which technically continues to this day. Staging the summit there gives Moon a bit of a home-field advantage, but the South Korean president seems intent on making sure Kim feels at ease, and has sequestered most of the media far away.

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WHO WANTS WHAT?

Here's where it gets complicated.

North Korea may want to use its new nuclear muscle, and the legitimacy it believes a Trump meeting will bestow, to win a peace treaty that ends the Korean War and eventually drives U.S. forces off the Korean Peninsula. It presumably hopes that will pave the way, in time, for a unified Korea that's led by the North and is beholden to neither the United States nor China.

That's one strain of thinking for the North's long-term dream, anyway; under current circumstances it's not likely that Washington would leave, given the bloodshed that occurred the last time North Korea thought there was a vacuum of power on the peninsula in 1950 and invaded the South.

In the short term, the skeptical argument goes that if the North can dangle disarmament in a series of meetings that follows these two summits, it could win more time — and an easing of crippling sanctions — to push forward in perfecting its weapons, while also collecting aid and concessions for nuclear promises that will never be met.

Seoul, on the other hand, wants to control the process, especially after the last year, when Trump repeatedly threatened a war that would overwhelmingly kill Koreans.

"We are preparing to take the leading role in a great transition in world history — a complete denuclearization of the Korean Peninsula, the establishment of a permanent peace and the sustainable development of relations between the South and North," Moon said recently.

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COULD THEY GET A REAL DEAL?

It is very unlikely that Kim is ready to give up his nuclear weapons — the benchmark for any real breakthrough on the Korean Peninsula. Kim, after all, is portraying his nation as finally being able, after years of suffering, to meet the United States as a nuclear equal.

But there are other measurements of success, and proponents of engagement say you'll never know what's possible until you sit down and talk.

Already the Koreas have set up a leaders' hotline, a big deal for countries that still spend a lot of time either not talking, aside from war threats, or communicating by fax.

One possible "get" could be if North Korea offers to freeze its weapons as a first step toward denuclearization, according to Robert Manning, a former State Department official, and James Przystup, with the National Defense University's Institute for National Strategic Studies. But, they wrote, Seoul and Washington must make clear that any freeze needs to come with unfettered U.N. inspections and visible dismantling of the North's nuclear infrastructure.

Ralph Cossa, a Koreas expert and president of the Pacific Forum CSIS think tank, is skeptical of any real breakthrough. The talks with Seoul are merely "a vehicle for pressuring Washington to talk," he said in an email. "From North Korea's perspective, the U.S. meeting is the real prize. Just holding the meeting enhances Kim Jong Un's legitimacy."

Even if no grand deal emerges, simply getting Kim in front of the world's cameras on South Korean-controlled territory could prove valuable.

The recent visit by South Korea's envoys to Pyongyang that set up the Trump meeting "has already told us more about Kim than we have learned over the past six years," Siegfried Hecker, the former director of the Los Alamos National Laboratory and a frequent visitor to North Korea's nuclear facilities, said on the Bulletin of the Atomic Scientists webpage.

And, he said, "it moved us at least one step away from the nuclear brink."

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Foster Klug, the AP's bureau chief for South Korea, has covered the Koreas since 2005. Follow him on Twitter at www.twitter.com/apklug