The sharp pivot to diplomacy with North Korea’s Kim Jong-un in early 2018 has rekindled longstanding dilemmas for South Korea and Japan. These two U.S. allies have come together during times of crisis on the Korean Peninsula, but they often have difficulty finding common ground when an opportunity for negotiation with Pyongyang emerges. South Korean President Moon Jae-in and Japanese Prime Minister Shinzo Abe continue to express their hopes for a close partnership as diplomacy with Kim evolves, but there remains ample room for missteps. In particular, outstanding territorial disputes, the continued salience of historical grievances in South Korea, and divergent perspectives on regional security following a potential peace regime on the Korean Peninsula set Seoul and Tokyo apart.
The Fault Lines That Remain
Several fault lines could complicate ongoing diplomacy with North Korea. The first is the ever-present politics of memory linked to Japanese military actions in World War II, as well as an outstanding territorial dispute between Japan and South Korea over islands in the Sea of Japan (or the East Sea, according to Seoul) that dates back to 1905. These islands, little more than rocky outcroppings, are known as Takeshima in Japan and Dokdo in South Korea. Seventy years have done little to diminish the need in South Korea to highlight the raw legacy of the past. Meanwhile, in Japan, conservatives and liberals alike now seem more willing to exacerbate old wounds than to find the salve to heal them.
Lingering historical tensions have made their way symbolically into recent Korean diplomacy as well, with Tokyo taking note. When U.S. President Donald J. Trump visited Seoul last fall, the Japanese government noticed that Dokdo shrimp were on the menu, a not-so-subtle reference to the territorial dispute. Similarly, Dokdo was evoked at the Moon-Kim summit, appearing in an image of a unified Korea on a piece of chocolate in the dessert course. The dispute compounds bilateral unease stemming from Korean attitudes toward a 2015 agreement on restitution for Korean women who were forced to serve in Imperial Japanese Army brothels during the Second World War, a deal negotiated by Moon’s impeached predecessor, Park Geun-hye.
Another possible fault line concerns military cooperation between South Korea and Japan, since political sensitivities have impeded this in the past. However, recent responses by Seoul and Tokyo to crises prompted by Pyongyang have been encouraging. In 2017, Moon and Abe found common cause in their responses to North Korean belligerence. Their respective military alliances with Washington have cemented a series of steps to ensure deterrence and to signal to Pyongyang their unwavering support for the U.S. military in case of a conflict.
Relatedly, negotiations between Seoul and Pyongyang have raised the prospect of a peace treaty to replace the armistice that ended the Korean War, leading to a broader cooperative framework for both Koreas. Today, the two allied militaries find common cause in the North Korean threat, but will they continue to do so if a peace treaty is concluded? How Seoul and Tokyo would see each other militarily in the absence of a sustained North Korean threat remains to be seen. Despite their longstanding cooperation with the United States since the end of the Korean War, these two countries cannot yet claim full confidence in one another.
Finally, South Korea and Japan could have fundamentally different views on the need for U.S. forces in Northeast Asia in the future. After the Moon-Kim summit, there was abundant speculation about what it meant for the future of U.S. forces on the Korean Peninsula. Days after the summit, Moon Chung-in, special advisor to the South Korean president, wrote that a peace regime would make it “difficult to justify [U.S. forces’] continuing presence in South Korea.” President Moon himself contradicted his advisor in a statement released soon after. Questions over the status of U.S. forces in South Korea are of great interest in Japan, as it would be gravely concerned if the U.S. military presence in the region, including the forces on the peninsula, were hastily reconfigured.
Can Seoul and Tokyo Coordinate Further Diplomacy?
Abe praised the Moon-Kim summit as a success, but past efforts at negotiation with the North have not always been easy for Seoul and Tokyo. This time, the breakneck pace and unpredictability of recent summitry have been particularly surprising for Tokyo. In a matter of months, North and South Korea have transitioned to a rapidly evolving diplomatic process. In the meantime, Kim also met with Chinese President Xi Jinping and began the process toward an unprecedented U.S.-North Korea summit.
In Beijing, Kim expressed interest in returning to the Six Party Talks. Following Kim’s agreement with Moon to seek a peace regime for the peninsula, Trump and Kim will be setting the contours for a denuclearization process, one that U.S. Secretary of State Mike Pompeo no doubt began to outline when he visited Pyongyang to meet Kim in early April and again in May. Amid these negotiations, Seoul and Tokyo will have different priorities in the Korea talks to come, and have shared their thoughts on these in recent weeks.
Moon and Abe have reason to take particular care with their consultations this time around. A far more unpredictable U.S. president makes it entirely possible that allied interests are secondary to the U.S. desire to end the nuclear weapons threat to its homeland. Instead of competing with each other for Washington’s attention, Seoul and Tokyo may find it useful to deepen their friendship to win greater leverage in U.S. decision-making. Regular Moon-Abe talks could reassure both countries that no compromise made with Kim would diminish the other’s security. In addition, they could compare notes on the future of Northeast Asia in the case of a Korean peace treaty. A longer-term Japan-South Korea dialogue would not only minimize opportunities for disagreement over relations with Pyongyang, but would also allow them to explore how best to engage China and the United States amid efforts to sustain peace in Northeast Asia.
A Reconfiguration of Northeast Asian Security?
The dramatic meeting between the two Korean leaders at Panmunjom has created excitement about a possible end to the state of war on the peninsula and the armistice that has militarily divided the countries since the end of the Korean War. A comprehensive peace settlement will mean a dismantling of the demilitarized zone and thus a reconfiguration of forces on the ground. Mattis, a thoughtful and measured spokesperson for the Trump administration, noted this when he said, “we are optimistic right now that there's opportunity here that we have never enjoyed since 1950,” suggesting that a Trump-Kim meeting may in fact have profound implications for the security architecture of Northeast Asia.
Japan cannot help but worry about this possibility. The approximately twenty-eight thousand U.S. forces in South Korea, largely ground forces, may head back to the United States. Some of these forces, however, are important to Japan’s security: the U.S. Air Force maintains its 8th and 51st Fighter Wings in South Korea and the U.S. Navy regularly visits Chinhae Navy Base near Busan. Removing them from the Korean Peninsula would remove an important layer of deterrence that Japan has relied upon in its own security calculations.
The unpredictable politics of the Japan-South Korea relationship are in part a result of opportunistic politics at home. This nationalist impulse has diminished opportunity for the two countries’ militaries to ensure sustained cooperation. One of the benefits of close allied military cooperation has been the development of a personal network among military leaders. Confidence and trust between South Korean and Japanese military officers will be vital as they navigate whatever comes in the years ahead.
Seoul and Tokyo have significantly different approaches to the rapidly shifting dynamics of Northeast Asian geopolitics, and here is where Moon and Abe have the most opportunity to shape their countries’ futures. Moon, Abe, and China’s premier, Li Keqiang, are meeting this week in Japan for the first Northeast Asian trilateral summit since 2015. Tensions between China and Japan have so far prevented this trilateral from serving the function intended when it began in 2008: to provide a forum for mitigating differences and building cooperation. In 2018, however, there is renewed optimism that these three countries can once more begin to build a foundation of common interest. Moon and Abe will have a chance to form their own understanding with China—one that does not seek to capitalize on historical grievances or on compromise with the North that could handicap their future ties.
The Tasks Ahead
The terms of the North-South peace regime for the Korean Peninsula and the military balance for the region are delicate topics, and perhaps it is too early to expect that South Korea and Japan can share a vision. For example, Seoul and Tokyo do not always share a common perspective on China’s ambitions in the region. And while transborder ties and economic opportunity should provide some solace in their approach to China, in today’s Asia, economic cooperation alone is insufficient.
This new phase of trilateral diplomacy between Seoul, Tokyo, and Washington will evolve as more is learned about Kim’s approach to the future of the Korean Peninsula. There will be much that Seoul and Tokyo can take issue with, but there is also much to lose by taking the easy road to recrimination and frustration. Moon, a South Korean progressive, and Abe, a Japanese conservative, are not natural partners, but they may be pragmatic enough to understand the costs of not working together effectively. Despite the excitement around a new, more peaceful future, it might be wise for each to consider what rapid changes to Northeast Asia’s security environment might bring. There is a window of opportunity here for South Korea and Japan to seize the benefits of their association as U.S. allies and plan how to sidestep the traps that await.