Historical grievances between America’s two closest Asian allies, Japan and South Korea, have loomed as a potential Achilles’ heel for U.S. security interests in the region for far too long. Lingering Korean resentment over the legacy of Japan’s colonial occupation, and Tokyo’s perceived reluctance to own up to that past, have undermined American attempts to present a united allied front in the Pacific.

This is no longer tenable. The security situation in the region has worsened, with Beijing’s massive military buildup, expansive territorial claims and threatening behavior toward Taiwan and its neighbors, as well as the growing nuclear and missile threat posed by its ally North Korea. The risks of war in Asia have become acute.

It is against this backdrop that President Biden will meet on Friday at Camp David with Prime Minister Fumio Kishida of Japan and President Yoon Suk Yeol of South Korea for the first-ever stand-alone leader’s summit between the three allies. The gathering is a pivotal opportunity that cannot be wasted. For the long-term stability and security of Asia, Mr. Biden must ensure that the leaders state unambiguously, and more firmly than ever, that they stand united.

A more united front between Japan, South Korea and the United States is much more than simply a military force multiplier. It is a geopolitical necessity at a time when countries like China and Russia are contributing to the rise of illiberalism, economic coercion and assaults on important global norms. The collective power of three of the world’s most important democracies, economies and technology leaders can serve as a bulwark for the rules-based international order — if they can maintain unity.

By choosing to hold the summit at Camp David, Mr. Biden has signaled that he understands the gravity of the moment. The historic presidential retreat outside of Washington has been the go-to venue for some of the most important U.S. diplomatic events. The Camp David Accords that laid the foundation for the end of hostilities between Israel and Egypt were brokered there in 1978, as were later peace talks between Israel and the Palestinians. Holding Friday’s meeting at the retreat appropriately places the event in that pantheon and conveys the importance of the trilateral partnership to audiences in the three countries and the rest of the world.

The good news for Mr. Biden is that the relationship between Tokyo and Seoul is improving. Mr. Yoon has made the politically risky decision to mend fences with Japan — a stance still unpopular with many South Koreans — and Mr. Kishida has responded positively. The factors behind this are complex, but they include a desire by both sides to align more closely with Washington as China looks to challenge U.S. power. In March, they held their nations’ first bilateral summit in 12 years. But this progress remains fragile and vulnerable to electoral politics. Previous attempts at moving past historical divisions have foundered with changes of government in the two countries.

Like Mr. Biden, the Japanese and South Korean presidents have important elections looming. Mr. Yoon, who took over in May 2022 and whose approval ratings have languished for most of his tenure, faces national assembly elections in the spring. Mr. Kishida is likely to call snap parliamentary elections by the end of the year and could face a leadership challenge within his own party. It is vital that the three leaders clearly convey to their own electorates — and to regional players like China — that their commitment to collective security is irreversible and will withstand domestic political changes.

As President Barack Obama’s special assistant and later assistant secretary of state for East Asia, I saw firsthand the disruptive effects of friction between Japan and South Korea. At times, it shut down defense exchange programs, meetings between officers, naval ship visits and joint military exercises. Reluctance to share real-time digital radar data about North Korean missile launches directly between defense systems in South Korea and Japan has required the U.S. military to employ cumbersome workarounds that could slow critical reaction time in the event of an attack.

China and North Korea have proven themselves adept at exploiting such differences. They continue to remind their people and those in the wider region of Japan’s colonial and wartime history, helping to keep alive memories that are also a source of anti-Japanese sentiment in South Korea. China imposed severe economic penalties on Seoul for its decision to deploy a defensive American antimissile system over Beijing’s objections. North Korea has in the past dangled the possible return of Japanese citizens said to have been abducted by Pyongyang decades ago, partly in an effort to curry favor with Tokyo and get it to ease some sanctions imposed on North Korea. Beijing has tried to sow local opposition in Okinawa against the U.S. military bases there.

The one-day summit is expected to result in more joint military exercises and other commitments to coordinate more closely. But the three-way relationship is deep and wide, and not limited to defense. For the Camp David summit to have maximum impact, it must make clear that the relationship is defined as more than just an alliance against China. As important leaders in trade, industry and innovation, the three countries have been working intensively on closer cooperation in vital issues like technology, supply chains and economic security, and the summit should produce a document that reviews the progress to date in these areas and lays out a vision for building on that.

Most importantly, Mr. Biden must ensure that the core messaging from Camp David is that the paradigm in Asia has changed. The people of the three countries, especially Japan and South Korea, must be made to realize that the security of each is inseparably linked and that none of them can ignore a threat or attack against the other. This will mean dispelling concerns over getting dragged into someone else’s fight. Some South Koreans, for example, worry that a conflict over Taiwan will require Seoul to extend military support to the United States and Japan, and that North Korea might be tempted to exploit that with aggression against South Korea. Some Japanese worry that escalating friction between Washington and Beijing over Taiwan could lead to a Chinese attack on bases in Japan. Differences like these play into the hands of China and North Korea.

The Biden administration has so far adroitly supported the steady improvement in relations between South Korea and Japan. He must lock in this progress at Camp David.

Daniel Russel is vice president for International Security and Diplomacy at the Asia Society Policy Institute in New York. He served as assistant secretary of state for East Asian and Pacific affairs under President Barack Obama.

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