South Korea’s Formal Membership in the Quad Plus: A Bridge Too Far?

Virtual Quad Summit, March 12, 2021. (Official White House Photo by Adam Schultz)

On September 24, the four leaders of the Quadrilateral Security Dialogue (“Quad”) countries held their first in-person summit, solidifying the partnership between the United States, Australia, India and Japan in the face of pressing issues facing the Indo-Pacific. Absent from the summit but alluded to in the joint statement was the Quad’s broader network of “like-minded partners,” termed the “Quad Plus.” In March 2020, the first Quad Plus meeting convened representatives from New Zealand, South Korea and Vietnam; while the agenda was originally limited in scope to coordinating COVID-19 approaches, the broader framework has been floated as a group of like-minded countries collaborating on a range of regional and global issues in line with the spirit and scope of the Quad leaders’ joint statement.

As the original Quad countries solidify their partnership, however, key obstacles persist to including South Korea as a formal member, a country with a longstanding interest in balancing between the US and China and a much greater interest in resolving the North Korea issue than any of the other six, save the United States. If South Korea were to join a consultative group based on the Quad Plus, it would constitute a dramatic shift in its foreign policy.

South Korea’s Strategic Calculation Toward a Quad Plus Consultative Framework

During President Moon’s visit to Washington in May 2021, the two sides’ joint statement explicitly mentioned the Quad, stating that they “acknowledge the importance of open, transparent, and inclusive regional multilateralism.” The statement also affirmed “support for enhanced cooperation with Pacific Island Countries,” which can be interpreted as leaving room for working with New Zealand.

Despite public statements allowing room for a strengthened Quad Plus, a South Korean decision to formalize its membership in the Quad would confront several thorny strategic and diplomatic challenges. South Korea’s strategic outlook on its relationships with North Korea, China and the other Quad members will define its openness to engaging publicly with any expanded Quad formation. It will be important for other current and prospective Quad Plus members to minimize the impact of these obstacles to permit South Korea to meaningfully take part in this multilateral security framework.

North Korean Denuclearization and Reunification

The effectiveness of cooperation in a multilateral framework is largely a function of the size of the group, its geographic distribution and the concerns and priorities of members. Seoul’s paramount domestic and strategic interest in addressing the North Korea nuclear issue poses a major obstacle to the expansion of the Quad format. The Republic of Korea (ROK)’s foreign policy is concentrated on the domestic, bilateral and multilateral matters associated with engagement with North Korea—a reality that will distinguish Seoul’s approach to the geographically distant Quad Plus partners and contrasts with their own willingness to pursue cooperation.

Seoul’s focus on the Pyongyang issue is evident in its public messaging. Hwang Ji-hwan, a presidential policy adviser, said that South Korea is considering joining Quad Plus to show its commitment to the US-ROK alliance and, indirectly, steer the US toward talks with North Korea. When it comes to agenda-setting and framing of Quad Plus cooperation, each capital’s diverse domestic and foreign policy priorities may impede meaningful coordination on the North Korea issue or—worse—could undermine South Korean or US efforts toward conflict resolution on the bilateral, trilateral or multilateral level. In other words, greater inclusivity could foster zero-sum competition over agenda-setting central to each party’s national security—ranging from India’s land border disputes with China and US concerns about strategic stability to Vietnam’s territorial disputes with China in the South China Sea. Seoul may fear that its multilateral involvement in discussing these matters could muddy the waters in solving the peninsular issues.

When the greatest security threat to the Korean Peninsula is internal, it is difficult to justify externalization of security cooperation without ample benefits to national security. And, in fact, this is one reason Seoul’s experience in joining networked security architectures remains nascent and unregularized. To move forward, Quad Plus promoters will need to provide South Korea with greater strategic incentives to join the group beyond whatever benefits it may see in membership to make progress on North Korea.

South Korea in the Middle of US-China Competition

South Korean foreign policy has consistently played an intricate balancing act between the US and China; the Quad and Quad Plus’s image as an instrument of the US Indo-Pacific strategy—or, more bluntly, as an anti-China coalition to contain Chinese power—may complicate this juggling act. In September 2020, then-Minister of Foreign Affairs Kang Kyung-wha underscored this reality, noting that, while South Korea remains “anchored” in the US-ROK alliance, China is its largest trading partner. She clearly stated that South Korea would need to “think very hard” about whether a Quad Plus would benefit Seoul’s national security interests. Kang’s successor, Chung Eui-yong, has maintained a similar stance on the Quad Plus, remaining receptive to partnerships that are transparent, open and inclusive. The subliminal meaning of “inclusive” could be read as not exclusionary or targeting any particular country, i.e., China, which is essential not only to South Korea’s trade, but also to making progress on North Korea.

At the Moon-Biden meeting, apart from a brief statement on maintaining cross-Strait stability, China was not mentioned—reflecting South Korea’s strong preference to avoid explicitly linking Quad cooperation to the China issue. Moon stated that Biden had not pressured him to take a tougher stance on Taiwan. Moreover, as a whole, despite the overwhelming US fixation on China in its foreign policy, the Moon-Biden meeting did not mention security issues, authoritarianism or competition among great powers. These omissions, combined with language about “seeking diplomacy with North Korea” and inter-Korean dialogue consistent with Biden’s North Korea policy review, spoke to South Korea’s balancing act, and do not bode well for a Quad Plus ostensibly aimed at containing China—at least not one with South Korean participation.

Japan’s Free and Open Indo-Pacific (FOIP) Concept

None of the three potential participants constituting the Quad Plus—New Zealand, South Korea or Vietnam—has publicly embraced an Indo-Pacific geographic realignment and/or aligned itself with the concept of a free and open Indo-Pacific region. Seoul, in particular, is in a difficult position, wedged between its current stances of not officially endorsing FOIP, maintaining a robust US-ROK alliance, and prioritizing the North Korea issue. Its own attribution of FOIP to Japanese regional strategy may even hinder applying the Quad’s emphasis on FOIP to the broader group; South Korean presidential aide Kim Hyun-chul stated in 2017, “Japan initiated the free and open Indo-Pacific idea, and it does not seem right for South Korea to join in the plan.” In short, Quad leaders can either delink the framework from FOIP to attract new members who have not endorsed this concept, or it can double down and risk further expansion and disagreements over key issues like what to call the region and whether to promote freedom and openness.

The US-ROK Alliance and ROK-Japan Relations

Apart from Japan, the United States has the most robust military-to-military ties and alliance structure with South Korea. In considering the Quad Plus, Seoul will weigh the potential benefits of a broader—and, therefore, potentially diluted cooperation framework—for its strategic ambitions and priorities. In this regard, the Quad Plus framework would not deepen security or related ties with any other regional party to the North Korea issue except Japan. Moon’s statements in May did emphasize trilateral cooperation, but they simply repeated previous commitments which hadn’t broken through the thorny politics of historical relations.

Tipping Points in South Korea’s Participation in the Quad Plus

President Biden came into office committed to strengthening US alliances and Indo-Pacific partnerships. As a leader of the Quad and a key South Korean ally, the United States could play an instrumental role in overcoming the challenges confronting Seoul if Washington is serious about transforming the Quad Plus into a multilateral security framework. A first step would be a clear understanding of the realistic avenues for deepened South Korean engagement in Quad-like frameworks. There are four factors that may tip the scales and promote deeper South Korean engagement with the Quad.

The ability of the Quad Plus to frame itself as a coalition working toward benign common goals. Given Seoul’s security interests and balancing act between China and the US, this would entail a generalized, non-China-focused framing of any Quad Plus dialogue. Just as with the original Quad, non-security-oriented issues of cooperation could be meaningful first steps to develop the multilateral relationship. Rather than necessitating adoption of FOIP or other grand commitments, collaboration could cover global health, technology or climate, all of which were productively identified in the September 24 joint statement on the Quad Summit.

Such engagement could most fruitfully take the form of regular behind-the-scenes, working-level consultations, either in a bilateral or mini-lateral format, followed when appropriate by more public meetings involving senior officials. The political contentiousness of the Quad concept and fears of Chinese retribution necessitate that any Quad Plus security framework has a pre-defined scope of cooperation prior to public engagement. While this would limit the depth of a Quad Plus security architecture, corralling New Zealand, South Korea and Vietnam to adopt a tougher stance will prove in the short term too large a shift in their strategic postures.

Significant progress on the North Korea issue. As long as denuclearization talks are stalled, Seoul remains dependent on Beijing’s unique leverage over Pyongyang and will continue to walk a fine line in any engagements labeled “Quad.” For Washington to pull Seoul into a Quad Plus framework, it will have to deepen engagement with Seoul on nontraditional security issues as well as make progress on North Korean denuclearization. Put simply, South Korea’s integration into the Quad would be a very heavy diplomatic lift for the Biden administration.

Political leadership in South Korea. The Democratic Party’s Moon Jae-in is ineligible for reelection in March 2022, ending a historically China-friendly and US-skeptical administration. As Moon famously wrote in 2017, South Korea should learn to “say no to the Americans.” On the other hand, Yoon Seok-yeol, the presidential favorite for the People Power Party (the conservative opposition party), has doubled down on its pro-US and China-critical roots. As Yoon said in July, “there must not be any light in South Korea-US relations, and given that close relation with the US, other countries like China will pay attention to us.” With the partisan split on the issue of US-China relations, the upcoming election will determine how South Korea balances between the US and China in the next five years. A conservative successor to Moon would shift South Korean policy closer to the US and keep discussions of South Korean participation in the Quad Plus alive.

The future of Chinese foreign policy toward South Korea. If the Chinese were to become significantly more aggressive toward South Korea or if “Chinese assertiveness trespasses upon Seoul’s foreign policy autonomy,” Seoul may be forced to reconsider the value of joining a Quad Plus structure. The two countries do have a minor maritime dispute over Socotra Rock (Ieodo) in the Yellow Sea (West Sea), and military tensions have not been unprecedented in the past decade. For example, warming relations between Seoul and Beijing briefly stalled when China extended its Air Defense Identification Zone in the East China Sea in 2013. And the Terminal High Altitude Defense (THAAD) controversy demonstrated to Seoul the pressure Beijing is willing to apply when it views its national security as jeopardized. Beijing reacted negatively to the Moon-Biden joint statement. But it remains to be seen how China’s relations with South Korea will evolve in the next couple of years—and whether a more aggressive posture could serve as a catalyst for stronger US-ROK relations. As Chinese military modernization progresses, there may be a point when South Korea’s security interests are threatened enough to consider greater Quad integration. This scenario, however, appears unlikely in the short-to-medium term.


South Korea’s equivocation on joining a Quad Plus security architecture illustrates the difficulties inherent in reaching consensus over policies among a growing number of diverse countries. If the Quad is committed to expansion, it must look beyond “like-minded-ness” as the connective tissue for a broader framework and consider each partner’s strategic interests. In the South Korean case, there is much to consider—and much to overcome.

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