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SEOUL, South Korea — In a year that began with President Donald Trump threatening to use his nuclear button against Kim Jong Un, the historic peace deal announced Friday between North and South Korea is all the more extraordinary.

The ambitious agreement pledges “no more war" and a common goal of the "complete denuclearization" of the Korean Peninsula.

There will also be an unprecedented summit between Trump and Kim, who has previously threatened to destroy both the U.S and South Korea.

It leaves many observers asking, "What’s the catch?"

Kim’s promise to end “the history of confrontation” appeared genuine, but analysts say there are several potential hazards for the United States in Friday’s deal.

‘Denuclearization’ in detail

The biggest will be reaching agreement on the precise definition of “denuclearization” and how it would be achieved or verified.

“North Korea cannot be trusted to denuclearize unless we know exactly what that means and under what conditions,” said Emil Dall, a research fellow at the RUSI think tank based in London. “This deal doesn’t give us any detail about that.”

While South Korea has no nuclear weapons, the U.S. has a major military presence in the country and Washington’s alliance with Seoul is a nuclear one — something that Pyongyang views as a threat.

Kim could demand a reduced American presence, an end to joint U.S.-South Korea military exercises or a change to the terms of their alliance. “That is something that Trump is unlikely to be able to offer,” Dall said.

“He has all the cards to play. Saying it is going to denuclearize is very easy for North Korea right now, which makes the detail of this deal very important.”

Kim’s readiness to negotiate suggests the North has successfully developed nuclear capabilities, Dall added.

“He has all the cards to play. Saying it is going to denuclearize is very easy for North Korea right now, which makes the detail of this deal very important.”

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A possible proposal could be a North Korean freeze of its weapons development ahead of later denuclearization.

Seoul and Washington will be pushing for any freeze to be accompanied by rigorous and unfettered outside inspections of the North's nuclear facilities, since past deals have crumbled because of North Korea's unwillingness to open up to snooping foreigners.

Legitimizing a rogue state

Even if Trump’s summit ends without further agreement, another risk is that it can be seen as normalizing a regime with a terrible human rights record.

“Kim has already achieved his aim of being taken seriously on the world stage,” said Dall. “Walking over the border with a handshake has allowed him to appear the peacemaker. It carries the risk that Trump ends up looking like the obstacle to peace on the Korean Peninsula.”

Kim’s confident appearance and message of progress — the first time he has ever spoken in front of the world’s press — increases pressure on the White House as the deal reaches its next, more complex phases.

Asia strife

All of which could further drive a wedge between the United States and South Korea — something that would in turn increase friction with China and Japan.

Tokyo gave a very cautious response to Friday’s deal. Japanese Prime Minister Shinzo Abe said the North-South talks were “a very positive sign” but noted that this was not the first time Pyongyang had pledged peace. “There have been other declarations in the past,” Abe said.

Takashi Kawakami, professor of international politics at Tokyo’s Takushoku University, said any dilution of the U.S.-South Korea alliance would ratchet up regional tensions.

"Japan would become the front line,” he said. “Japan's security risks would increase. The Chinese navy would probably come into the Sea of Japan, as would the Chinese air force.”

Beijing applauded Friday’s words, but it remains wary of a unified Korea that could have closer ties to the United States and it could still upend any deal.

Pressure for more pressure

Trump will find himself caught between a personal desire to reach a peace deal and the views of hardliners who believe North Korea has already done enough to deserve a military response.

Such critics are unlikely to accept any weakening of sanctions on the regime, even though Friday’s promises of cross-border trade and economic cooperation would almost certainly require sanctions relief.

Trump administration officials are adamant that a military option is still on the table if the Friday’s peace deal comes to nothing. White House adviser Kellyanne Conway indicated Friday that Trump had room to back out of the summit with Kim. “If the conditions are not right, then the United States will reconsider,” she told reporters. “But so far, so positive.”

Past performance

The record of deals involving North Korea is not encouraging. Its previous leaders have used high-profile peace overtures to buy time for further weapons development in the past and they may be doing so again.

President Bill Clinton’s Secretary of State, Madeleine Albright, held talks with Kim’s father, Kim Jong Il, in 2000 but efforts ultimately failed.

Friday’s three-page declaration is “breathtaking in its scope and ambition,” said David Albright, president of the Institute for Science and Security in Washington. "But how to achieve all the goals laid out in the document, given the current situation? Unless a firm foundation and plan for North Korea's complete verified irreversible nuclear disarmament is laid out with a relatively short schedule, most of the other commitments in the declaration are merely wishes.”

However, Kim appeared to address these concerns in his opening remarks at Friday’s meeting.

“As expectations run high, there are also skeptical views,” the North Korean president said. “Extensive agreements were concluded in the past, but we failed to put them into practice for over a decade.”

In contrast, Kim said, Friday’s deal was the product of strong momentum toward agreement. “If we move forward hand-in-hand with firm determination,” things will get better, he promised.

Alastair Jamieson reported from London, and Mac William Bishop from Seoul.