North Korean leader Kim Jong Un and U.S. President Donald Trump in Singapore. June 12, 2018. (Anthony Wallace/AP)

Moon Chung-in is a distinguished professor at Yonsei University and the special advisor for unification, diplomacy and national security affairs for South Korean President Moon Jae-in.

SEOUL — For all the fears of a diplomatic catastrophe, the Singapore summit was a remarkable success. After a precarious rollercoaster ride to get there, U.S. President Donald Trump and North Korean leader Kim Jong Un reached a historic agreement on how to resolve the protracted North Korean nuclear quagmire.

While Kim made his “firm and unwavering commitment to complete denuclearization of the Korean Peninsula,” Trump reciprocated by committing himself to a security guarantee. For all of the drawbacks — such as the absence of timelines and an explicit statement on complete, verifiable and irreversible denuclearization — the prospects for a peaceful resolution of the North Korean nuclear problem have now become all the more likely, while the danger of a military crisis has faded away.

But now comes the next set of challenges — the devil, as they say, is in the details. Commitment for commitment is one thing, but action for action another, and implementing mutual pledges presents its own perilous odyssey. As we move into this next phase, the efforts of Trump and Kim alone will not be sufficient for the task, and it is critical to look to neighboring countries and the region as a whole.

The Singapore deal brings mixed blessings to countries in Northeast Asia. All of them see it as a remarkable breakthrough of the nuclear stalemate, but worries and anxieties have emerged.

The South Korean government seems to be a major beneficiary. Because Trump and Kim agreed on not only denuclearization but also on a robust and lasting peace regime, South Korean President Moon Jae-in can now expedite inter-Korean exchanges and cooperation as well as his plan to produce a tripartite declaration by Seoul, Pyongyang and Washington to proclaim an end to the Korean War and pave the way to a permanent peace on the Korean Peninsula.

Conservatives in South Korea worry about the fate of the South Korea-U.S. alliance and the continuing presence of American forces in South Korea, as ties between Pyongyang and Washington are to be improved to an unprecedented degree. However, the Singapore deal does not affect the status of the alliance and the presence of American forces until North Korea completes its denuclearization.

For their part, China, Japan and Russia are concerned by being left out by the Pyongyang-Washington deal. As a legal party to the Korean Armistice Agreement, China believes it should be included in any negotiations on the change of its status and peacemaking on the Korean Peninsula. Also, as host and champion of the six-party talks, Beijing claims a diplomatic stake in the peace process and the issue of denuclearization. Tokyo, meanwhile, could worry about being passed over, because its national interests, such as its fear of North Korea’s nuclear and intermediate-range missile threats and the ongoing issue of Japanese citizens who were abducted by North Korea, were not fully addressed at the Singapore summit. Russia shares similar fears.

Such worries and anxieties, while understandable, are overblown. There is no cause for Beijing’s concerns. The reason is that the Singapore process is, in fact, predicated on the suspension of both North Korea’s nuclear and missile activities and the combined South Korea-U.S. military exercises and training, as well as the parallel pursuit of North Korea’s denuclearization and the signing of a peace treaty — exactly what Beijing has been advocating. Any attempts to formally end the Korean War and to forge a new peace regime wouldn’t be conceivable without Beijing’s participation.

In fact, China’s role is likely to become even more pronounced after the Singapore deal. The United States badly needs China’s economic leverage to make North Korea’s denuclearization sustainable, in both a positive and negative sense.  Beijing’s compliance with United Nations sanctions resolutions is pivotal to the enforcement of the constraints keeping Pyongyang on the path to denuclearization. Beijing can also serve as Pyongyang’s reliable partner and a hedge against any backsliding by the United States in implementing its political, military and economic assurances. Thus, China cannot be sidelined.

The Singapore deal should be backed up by corresponding supplies of energy and economic compensation. Thus, bilateral and multilateral economic cooperation in the fields of energy, trade and investment is inevitable. But Trump made it clear that the United States is not going to give economic assistance to North Korea. There is no Marshall Plan in the works for Pyongyang. Trump even suggested that South Korea, Japan and China should be the countries that extend economic assistance to North Korea because of their economic and functional proximity. This dovetails with Trump’s own vision of making America safe without spending a single penny.

This being the case, the roles of Japan and Russia, along with those of South Korea and China, come back into center view. In fact, North Korea can expect large sums in reparations as well as economic development assistance from Japan to compensate for damages incurred during Japan’s brutal colonial occupation of Korea during the first half of the 20th century. Japan cannot be left out. The same can be said of Russia, whose abundant energy resources in the Russian Far East can greatly contribute to meeting North Korea’s energy needs. South Korea and Russia are currently working together to develop energy resources in Siberia, efforts which could significantly benefit North Korea.

The Singapore deal represents the triumph of bilateral summit diplomacy. Trump has opened the gates to progress in a way none of his predecessors — Democrat or Republican — were willing or able to. But going forward, the United States alone cannot manage the North Korean nuclear issue in the post-summit period. It should seek a more inclusive approach by working closely with South Korea, China, Japan and Russia. Even the United Nations, the European Union and other powers such as Australia, Singapore and India should be invited to help tackle the daunting challenges. A multilateral approach is the only viable way to resolve the North Korean nuclear problem with a win-win outcome.

A six-party summit involving North and South Korea, the United States, China, Japan and Russia could offer a stable structure to advance the achievements of the Singapore summit by supplementing bilateral and trilateral summit diplomacy. This historic opportunity must be seized by all if the promise of the Singapore summit is to be achieved.

This was produced by The WorldPost, a partnership of the Berggruen Institute and The Washington Post.