Photo: Tr3/Adobe Stock
In March 2025, General Romeo Brawner, chief of staff of the Armed Forces of the Philippines, suggested expanding the emerging “Squad”—an informal quadrilateral security initiative comprising the Philippines, the United States, Japan, and Australia—by inviting South Korea and India to join. First operationalized through joint maritime patrols in April 2024 within the Philippines’ exclusive economic zone (EEZ), the Squad reflects a growing emphasis on coordinated defense strategies in response to intensifying maritime tensions and territorial disputes in the Indo-Pacific. For South Korea, a country deeply integrated into regional security architectures and longstanding alliance frameworks, the proposal presents a strategic opportunity laden with diplomatic complexity. But while Seoul in some ways appears to be a natural fit for the Squad, its interest and ability to formally join the grouping is tempered by domestic political instability and a cautious approach toward regional alignment.
One of the most compelling drivers for South Korea to consider joining the Squad lies in its strategic convergence with the grouping’s vision for the Indo-Pacific. Seoul’s Free, Peaceful, and Prosperous Indo-Pacific Strategy, explicitly recognizes that its national interests are deeply intertwined with regional stability and prosperity. The strategy emphasizes South Korea’s commitment to upholding a rules-based international order and enhancing regional security and economic connectivity in partnership with like-minded countries, including Association of Southeast Asian Nations members. This strategic outlook closely mirrors the Philippines’ own position in recent years, particularly in relation to maritime disputes, freedom of navigation, and multilateral security cooperation in the region.
Building on this shared strategic vision, South Korea and the Philippines have deepened bilateral ties and gained momentum for security cooperation. In October 2024, presidents Yoon Suk Yeol and Ferdinand Marcos Jr. elevated bilateral ties to a “strategic partnership,” underscoring a mutual intent to strengthen defense collaboration amid an increasingly complex regional security environment. In the signed memorandum of understanding, South Korea reaffirmed its support for the 2016 South China Sea arbitral ruling and its commitment to upholding a maritime order anchored in the United Nations Convention on the Law of the Sea. The two sides also agreed to enhance maritime security coordination through joint patrols, intelligence sharing, and cooperative maritime law enforcement. This level of political commitment provides a solid bilateral foundation for South Korea’s engagement with the Squad and positions Seoul as a strong candidate for the grouping.
Even more critically, South Korea has been instrumental in the long-term modernization of the Philippine Navy, demonstrating Seoul’s tangible influence in regional security affairs through sustained investments in shipbuilding, technology transfers, and equipment delivery. The South Korean shipbuilder HD Hyundai Heavy Industries (HD HHI) has been supplying advanced warships to the Philippines since 2016, and is expected to deliver at least 12 vessels by 2028, laying the foundation for a multi-layered maritime force capable of both littoral defense and extended blue-water operations. At the same time, South Korea’s strategic investments in Subic Bay, a critical maritime hub, have reinforced the bilateral foundation for maritime security and defense industrial cooperation. In 2024, HD HHI signed a long-term lease agreement with Philippine authorities to operate part of the Subic Bay shipyard, pledging approximately $550 million in investment over the next decade to revive local shipbuilding and maintenance capacity.
Backed by shared strategic principles and growing defense cooperation, Seoul has emerged as a trusted regional security partner and appears well-positioned to participate in the Squad framework. But domestic political turbulence and perceived risks to its carefully balanced regional relations make Seoul cautious about getting involved.
Since the failure of President Yoon’s martial law declaration in December 2024 and his subsequent impeachment, South Korea has plunged into protracted political turmoil that has significantly disrupted its capacity to engage diplomatically and coordinate effectively on security affairs. Japanese defense minister Gen Nakatani postponed his scheduled visit to Seoul in late December 2024, followed by the deferral of Prime Minister Shigeru Ishiba’s planned January 2025 trip. Then-defense secretary Lloyd Austin canceled his December 2024 visit, and his successor, Pete Hegseth, excluded South Korea from his first official tour of the Indo-Pacific in March 2025, choosing instead to visit Japan and the Philippines. These decisions underscored an unfortunate reality: with South Korea’s acting president and cabinet officials set to leave office within months, any engagement with them was likely considered inconsequential.
With the presidential election approaching, South Korea may be on the path to renewed political stability. However, even after a new administration takes office, the country is likely to remain in a transitional phase, which could continue to hinder the conduct of routine diplomatic functions. Potential shifts in foreign policy objectives and the absence of fully operational leadership may prompt Seoul to adopt a more measured and restrained approach to new regional security engagements. Moreover, restoring policy continuity and rebuilding strategic cooperation disrupted by recent political turbulence will require sustained and deliberate efforts. During this period of recalibration, South Korea may lack the bandwidth to engage with regional defense mechanisms that require timely coordination and strategic alignment among member states.
This risk-averse diplomatic posture is also evident in South Korea’s recent response to tensions in the Yellow Sea with China. In response to Beijing’s installation of large steel structures within the jointly administered Provisional Measures Zone, Seoul expressed “deep concern” and reaffirmed its lawful maritime rights, but has carefully avoided escalation that could jeopardize broader bilateral relations. Seoul also remains committed to maintaining constructive communication through all diplomatic channels and is particularly cautious about allowing maritime disputes to disrupt relations with Beijing ahead of Chinese president Xi Jinping’s anticipated visit later in 2025.
Such restraint is emblematic of a broader strategic calculus in Seoul’s foreign policy. In its Indo-Pacific Strategy, South Korea described Beijing as a “key partner for achieving prosperity and peace,” promoting a vision of an “inclusive” regional order that “does not seek to target or exclude any specific nation.” A similar approach informs Seoul’s cautious stance toward the Quad – Australia, India, Japan, and the United States – toward which it has favored functional and sectoral cooperation over a formal alignment that might be perceived as provocative. Its hesitation reflects concern not only over immediate tensions, also a broader risk management strategy aimed at preserving maneuverability and regional stability.
Amid an evolving Indo-Pacific security landscape, the binary question of whether South Korea will or will not join the Squad may not be the defining factor in shaping its regional role. Rather, it is the nature, content, and continuity of its cooperation with like-minded partners that will likely prove more consequential. Seoul has already demonstrated meaningful commitment, consistently advocating for the importance of international law and supporting Philippine defense modernization. Even without a formal mechanism, shared strategic outlooks offer a firm foundation for expanded collaboration. South Korea’s current low-profile posture may not reflect strategic retreat, but a conscious effort to balance flexibility with risk management. Exploring informal or functional avenues of engagement, such as enhancing maritime domain awareness, defending lawful maritime rights, and promoting rules-based cooperation, could enable Seoul to strike a balance between active regional participation and strategic autonomy.
Ziya Guo is a research intern with the Asia Maritime Transparency Initiative at the Center for Strategic and International Studies in Washington, D.C.