On July 11, 2025, South Korea, the United States (U.S.), and Japan conducted a joint air exercise as part of their efforts to strengthen their joint responses against North Korea’s nuclear and missile threats. The exercise took place in international waters off the coast of Jeju Island, located in southern South Korea, and involved at least one U.S. B-52H bomber, as well as South Korea’s KF-16 and Japan’s F-2 fighter jets. This marked the first deployment of the strategic bomber near the Korean Peninsula this year.[1] U.S. Chairman of the Joint Chiefs of Staff General Dan Caine stated, “Our focus in the United States is to reestablish deterrence, and in order to do that, we need cooperation among the three countries.”[2]
The trilateral security cooperation between South Korea, the United States, and Japan functions as a complementary mechanism at the point where the understanding of multilateral security in the Asia-Pacific region falls short. Furthermore, it has served as a balancing factor against the joint military activities of China, North Korea, and Russia in the region. Trilateral security cooperations extend beyond joint military exercises through regular summits and meetings, facilitating the establishment of diplomatic consultation mechanisms. In this way, the dialogues developed within the framework of defense and security understanding enhance diplomatic alignment among the countries and lead them to act in coordination.
On July 28, 2024, the defense ministers of Japan, the United States, and South Korea reached an agreement on a significant security cooperation framework that would assist in the “institutionalization” of trilateral defense relations and make their reversal more difficult.[3] This meeting, which played a critical role in the process leading to security cooperation, has been influential in enabling allied forces to establish a long-term security mechanism. Moreover, it has served as a model of a “minilateral” security network for other U.S. allies in the Asia-Pacific, such as Australia and the Philippines, as well as for member states of the Association of Southeast Asian Nations (ASEAN).
In this context, minilateralism has manifested itself through the South Korea–U.S.–Japan trilateral alliance in response to China’s growing influence and presence in the region, as well as North Korea’s nuclear activities. Formations such as the Quadrilateral Security Dialogue (QUAD) and AUKUS also align with minilateral structures, supporting the development of multi-layered security networks. Minilateral frameworks play a role in enabling quicker and more effective responses to regional challenges, while also reflecting the United States’ “burden-sharing” strategy. In this way, the South Korea–U.S.–Japan trilateral mechanism stands out as a key actor in shaping or rebuilding the regional security architecture.
The U.S. National Defense Strategy (NDS) prioritizes strengthening these relationships by increasing burden-sharing with allies and partners around the world, thereby creating the necessary conditions for lasting peace.[4] The burden-sharing strategy, which is also effective in building a shared peace, guides in a new era for maintaining security balances in the Asia-Pacific and reinforcing multilateral diplomatic dialogues.
Operating on a consensus-based decision-making mechanism and due to its members tending toward more individual or bilateral and trilateral defense- and strategy-focused arrangements (such as the comprehensive strategic partnership between Vietnam and the U.S., and Malaysia and Singapore reaching an agreement on an “indicative timeline” to determine the precise maritime boundaries in the Johor Strait),[5] ASEAN countries have been unable to take a clear stance on security. Consequently, regional security has become open to multilayered and non-aligned structures. In other words, multilateral platforms like ASEAN, which are large and involve many countries, make it difficult to reach definitive conclusions due to their consensus-based nature. Indeed, minilateral structures, which enable a smaller number of countries to focus on specific issues and make joint decisions more quickly, facilitate the implementation of more effective security measures, especially with the involvement of external actors such as the United States. Some ASEAN countries, including Vietnam and the Philippines, are also enhancing their defense capacities by cooperating with powerful actors in line with their security interests.
In conclusion, the security cooperation developed among South Korea, the United States, and Japan is reshaping defense and security in the Asia-Pacific region, particularly in light of nuclear concerns, as observed in the tendencies of countries within the region. Furthermore, the regular meetings held between the parties not only contribute to institutionalizing this alliance but also set an example for other countries in the region.
Moreover, minilateral cooperations are becoming increasingly widespread, rendering the region’s security multilayered and giving rise to smaller but more effective alliances. This development will reinforce security structures capable of making faster and more coordinated decisions. Thus, contrary to the understanding that stability can be achieved through multilateralism, minilateral frameworks enable burden-sharing to come into play, allowing for more concrete and effective solutions to be produced.
Particularly, these minilateral structures serve as balancing factors against major powers like China, whose influence is growing in the region; by preventing the emergence of significant power vacuums and reducing uncertainty, they play a vital role in maintaining stability. Through these mechanisms, the balance of power is preserved, fostering an environment of stability in the Asia-Pacific.
[1] “S. Korea, U.S., Japan stage joint air drills involving B-52 bomber” Yonhap News Agency, https://en.yna.co.kr/view/AEN20250711004451315?section=national/defense, (Date Accessed: 13.07.2025).
[2] ” Top U.S. military officer calls for trilateral cooperation amid military buildup by N. Korea, China” Yonhap News Agency, https://en.yna.co.kr/view/AEN20250711003052315?section=national/defense, (Date Accessed: 13.07.2025).
[3] “U.S., Japan and South Korea ink deal to ‘institutionalize’ security ties”, Japan Times, https://www.japantimes.co.jp/news/2024/07/28/japan/politics/japan-us-south-korea-trilateral/, (Date Accessed: 08.07.2025).
[4] “Statement on the Development of the 2025 National Defense Strategy”, U.S. Department of Defense, https://www.defense.gov/News/Releases/Release/Article/4172735/statement-on-the-development-of-the-2025-national-defense-strategy/, (Date Accessed: 13.07.2025).
[5] “Malaysia, Singapore Chart Progress On Maritime And Airspace Disputes” Business Today, https://www.businesstoday.com.my/2025/01/08/malaysia-singapore-chart-progress-on-maritime-and-airspace-disputes/, (Date Accessed: 13.07.2025).
