Rethinking Regional Order: East Asia’s Strategic Realignment Amid U.S. Uncertainty

By Megan Wei, University of Chicago

Since the end of World War II, the United States has played a significant role in shaping security across East Asia. Through the establishment of bilateral alliances and long-term military presence, it has contributed to regional stability by deterring potential conflict and creating the conditions for the region’s economic growth. Within this framework, countries like Japan, South Korea, and Taiwan were able to prioritize domestic development while relying on the United States for overarching security. That system, however, is now under increasing strain. Beijing has expanded its military presence, used economic leverage to apply pressure on other nations, and taken a harder stance against Taiwan. At the same time, the United States is reassessing its global commitments, and domestic polarization has raised doubts about its future engagements abroad. These shifts have left many allies unsure of how much longer the existing order can hold. In response, Japan, South Korea, and Taiwan have begun pursuing more independent security strategies, not to distance themselves from the United States but to avoid overdependence on it. Over the past decade, they have worked to diversify their economies, invest in advanced technology, and strengthen regional partnerships to protect their interests in a changing security landscape. These efforts point to a broader shift. Instead of playing a secondary role in a U.S.-dominated system, countries like Japan, South Korea, and Taiwan are starting to act with greater autonomy within an order that still relies on American leadership but is becoming more multipolar. This emerging multipolarity has far-reaching implications. It can encourage stronger cooperation among Asian states and lead to more diverse regional security partnerships, but it also complicates how countries manage their relationship with China and maintain stability amidst growing strategic competition. 

The United States has long organized its security relationships in East Asia through a "hub-and-spokes" alliance system, building separate bilateral ties with key partners rather than pursuing a multilateral framework. After signing the U.S.-Japan Security Treaty in 1951 and the U.S.-South Korea Mutual Defense Treaty in 1953, the United States reinforced its presence by establishing permanent military bases and stationing around 50,000 troops in Japan and 28,500 in South Korea.¹ Beyond maintaining troops on the ground, the United States has conducted regular large-scale joint military exercises, such as Operation Foal Eagle with South Korea and Keen Sword with Japan, to strengthen military readiness and cooperation.² Its commitment to Taiwan, reaffirmed through the Taiwan Relations Act of 1979, has also remained active, with continued arms sales, including an $8 billion F-16 fighter jet deal in 2019 and upgrades to Taiwan's missile defense systems.³ These efforts have not only offered U.S. security guarantees but have also tied the United States closely to the defense planning of its allies in the region. Yet, as new threats emerge and internal challenges grow, regional actors have begun to ask whether they can rely on American leadership with the same certainty they once did.

One of the most serious challenges to the traditional security order has come from China’s growing assertiveness. In the South China Sea, China has deployed advanced missile systems and carried out aggressive maritime patrols that challenge freedom of navigation. Additionally, tensions continue to rise in the Taiwan Strait as Beijing conducts periodic live-fire exercises and military flights near Taiwan’s airspace in an effort to intimidate Taipei. Along with its military actions, China has used economic coercion against countries that oppose its strategic interests, such as restricting exports to South Korea after the deployment of the THAAD missile defense system.⁴ Meanwhile, uncertainty about U.S. reliability has grown. President Donald Trump’s openly questioning of alliance commitments, particularly his demands in 2019 and 2020 that South Korea and Japan sharply increase their financial contributions for hosting U.S. troops, unsettled traditional security partners by raising fears that Washington might scale back its military presence if its demands were not met.⁵ Trump’s abrupt decision to suspend joint U.S.–South Korea military exercises following the 2018 Singapore summit with Kim Jong-un, along with reports that his administration considered withdrawing American troops from the Korean Peninsula, further illustrated the fragility of U.S. security guarantees in the eyes of regional allies.⁶ These actions signaled a broader shift in how the United States might view its alliances, raising new doubts about whether long-standing security arrangements could still be taken for granted by partners such as Japan, South Korea, and Taiwan.

As strategic uncertainty in the Indo-Pacific grows, Japan has begun to reorient its security posture, not to move away from the United States, but to reduce its reliance on a single partner. Over the past decade, Japan has conducted major national security reforms, most notably the reinterpretation of Article 9 of its constitution in 2015 to allow for limited forms of collective self-defense.⁷ This marked a turning point in Japan’s postwar approach to security, loosening long-standing constraints and creating the legal basis for a more active defense policy. Since then, Japan has steadily increased defense spending and expanded its military capabilities in response to mounting regional threats. In December 2022, the government announced a $320 billion defense plan aimed at raising military expenditures to 2 percent of GDP by 2027.⁸ Recent initiatives include the acquisition of long-range strike capabilities, co-development of sixth-generation fighter aircraft with the United Kingdom and Italy, and the development of hypersonic weapons.⁹ It has also relaxed long-standing restrictions on arms exports, authorizing transfers such as Patriot missiles to the United States and considering deals with other partner countries.¹⁰ These moves point not only to military modernization but to a more assertive defense posture that aims to build strategic capacity beyond the U.S. alliance alone. 

At the diplomatic level, Japan has broadened its security partnerships through the signing of Reciprocal Access Agreements (RAAs) with Australia in 2022, the United Kingdom in 2023, and the Philippines in 2024.¹¹ These deals allow for joint training and military coordination, making it easier for troops from each country to operate in one another’s territory. The agreement with the Philippines stands out as Japan’s first in Asia, and reflects a meaningful shift in how Japan is approaching regional defense. In addition to these bilateral agreements, Japan has intensified its diplomatic outreach to India and Southeast Asian nations. Its relationship with India has grown through regular 2+2 ministerial dialogues that focus on maritime security and defense cooperation, underscoring a mutual commitment to maintaining a free and open Indo-Pacific region.¹² In Southeast Asia, Japan participates in regional forums such as the ASEAN Regional Forum and the East Asia Summit, where it continues to promote international norms like freedom of navigation and peaceful conflict resolution.¹³ It has also offered maritime training and support to ASEAN member states, contributing to their security capacity. These moves suggest that Japan is starting to take a more active role in shaping the region’s security. Japan’s growing military capabilities and diversification of security partnerships mark a broader shift towards a more multipolar Asia that is less reliant on any single power to maintain order. While the alliance with the United States remains crucial, Japan’s strategy reflects an understanding that regional stability now depends on shared responsibility and not unilateral protection. In doing so, Japan not only strengthens its own security but also contributes to a more balanced regional order that may address Asian-specific crises on its own terms. 

South Korea has also adjusted its strategic posture in response to shifting regional dynamics. Like Japan, it has sought to increase its autonomy without stepping away from the U.S.-led order. Under President Moon Jae-in (2017–2022), South Korea pursued a more flexible foreign policy that aimed to reduce strategic dependence on any single power. Through the New Southern Policy, South Korea expanded diplomatic and economic engagement with Southeast Asia and India, seeking to diversify its regional ties beyond the U.S.-China binary.¹⁴ In addition to this diplomatic outreach, South Korea increased investment in its defense capabilities. Notably, it launched the KF-21 Boramae fighter jet program, which completed its maiden flight in 2022 and is expected to produce 120 aircraft by 2032.¹⁵ It also completed development of its long-range surface-to-air missile system (L-SAM), designed to intercept ballistic missiles at high altitudes, with production planned for 2025.¹⁶ South Korea has set an ambitious goal to become the world’s fourth-largest arms exporter by 2027 in order to strengthen its defense industry and reduce dependence on foreign suppliers.¹⁷ These steps show that South Korea has been trying to take on more responsibility for its own security, both nationally and within the region. Under Moon, the government handled its relationship with China cautiously by trying to keep economic ties stable and avoiding open conflict. At the same time, it held firmly to its defense relationship with the United States. Thus, none of this suggested a break from the alliance. Instead, it reflected an effort to give South Korea more room to make its own choices while keeping the U.S. partnership in place.

Since taking office in 2022, President Yoon Suk Yeol has reemphasized the importance of the U.S. alliance while also pushing South Korea to take a more active role in regional security.  In 2023, Yoon and President Biden announced the Washington Declaration, which established a Nuclear Consultative Group and committed to the rotational deployment of U.S. strategic assets on the Korean Peninsula to reassure South Korean security concerns amid growing North Korean threats.¹⁸ Additionally, Yoon has prioritized trilateral coordination with the United States and Japan. At the Camp David summit, the three countries agreed to hold regular joint military exercises and meet annually for high-level security consultations.¹⁹ Although Moon and Yoon took different approaches, both worked toward the same goal, which was strengthening South Korea’s security while finding more room to maneuver in a rapidly changing Indo-Pacific. Instead of stepping away from the U.S.-led order, Seoul has adapted how it operates within it. At times, this has meant building new regional partnerships or investing in its own defense. At other times, it has reinforced its core alliance with Washington. However, this balance may again be tested by domestic politics. The rise of opposition leader Lee Jae-myung, whose platform is viewed as more accommodating toward China and Russia, has introduced new uncertainty about the direction of South Korea’s foreign policy. As political divisions deepen at home, Seoul’s next administration could face renewed questions about how to navigate its position between the United States, China, and other regional powers. Across East Asia,  such internal shifts highlight how domestic politics increasingly shape the evolving multipolar security landscape. 

Taiwan, too, has responded to intensifying regional pressures by strengthening its resilience while deepening its ties with the United States. In 2024, Taiwan raised its defense budget to a record $19.1 billion, which represents approximately 2.5 percent of its GDP.²⁰ At the heart of Taiwan’s defense planning is the “Overall Defense Concept,” which focuses on using asymmetric tactics to make any potential attack from China costly and difficult to carry out.²¹ This approach focuses on making any invasion costly and complex for the Chinese. A number of recent developments reflect Taiwan’s shift away from traditional defense models and toward a more flexible approach. In 2025, Taiwan began sea trials for the Hai Kun, its first domestically built submarine.²² This marks a major step in strengthening undersea defense and reducing dependence on foreign technology. The submarine program also signals Taiwan’s growing emphasis on building self-sufficiency in critical areas of military capability. In addition, Taiwan received the first batch of U.S.-supplied Harpoon Coastal Defense Systems in late 2024, which significantly boosted its ability to counter naval incursions in the Taiwan Strait.²³ To complement this system, Taiwan has also continued to deploy its own Hsiung Feng III supersonic anti-ship missiles, adding another layer to its maritime defenses and strengthening its ability to respond to threats at sea.²⁴ These moves demonstrate a clear investment in credible deterrence and reflect a broader commitment to adapting Taiwan’s military to the evolving nature of cross-strait threats.

Simultaneously, Taiwan has accelerated efforts to diversify its economy and reduce dependence on mainland China, its largest trading partner. Through agreements like the U.S.-Taiwan Initiative on 21st-Century Trade and strengthened economic ties with the European Union and Indo-Pacific partners, Taiwan has sought to integrate more deeply into global supply chains.²⁵ At the center of this strategy is Taiwan Semiconductor Manufacturing Company (TSMC), whose global role has only expanded in recent years. In 2025, TSMC announced it would invest an additional $100 billion in its U.S. operations, bringing its total commitment to $165 billion.²⁶ This expansion includes plans for three new fabrication plants, two advanced packaging facilities, and a major R&D center in Phoenix, Arizona, making it the largest single foreign direct investment in U.S. history. The project is expected to create tens of thousands of high-skilled jobs and generate over $200 billion in indirect economic output across the country over the next decade. By moving part of its production base abroad, TSMC is not only strengthening economic ties between Taiwan and the United States but also helping Taiwan reduce its exposure to economic coercion from Beijing.²⁷ These efforts are meant to protect Taiwan’s lead in advanced technology and reduce the risks it faces from growing pressure by China. However, recent tensions between Washington and Taipei over TSMC’s overseas expansion underscore the complexities of this economic interdependence. Taiwanese officials have expressed concern that shifting too much chip production to the United States could erode Taiwan’s strategic advantage. This tension reflects a broader regional trend in which U.S. tariffs and shifting global supply chains have also pushed Asian economies such as Japan, South Korea, and ASEAN states to deepen trade and investment ties with one another. As growing economic cooperation potentially translates to greater strategic coordination, Washington’s inconsistency may have paradoxically encouraged Asia to strengthen its own regional resilience. Despite these developments, Taiwan’s international security still relies heavily on U.S. support. The United States continues to be the primary supplier of advanced arms to Taiwan, including recent sales of F-16 fighter jets and other defense systems.²⁸ American naval patrols in the Taiwan Strait, alongside expanding unofficial diplomatic engagement and deepening supply chain cooperation, continue to reinforce Taiwan’s position in the regional order. While Taiwan has worked to strengthen its economy and defense, its long-term security still depends on the strength of U.S. support and the continued presence of American leadership in the region.

As President Trump begins his second term, longstanding questions about the reliability of American leadership in East Asia have become more pressing. His earlier push for allies like Japan and South Korea to shoulder a greater share of their defense costs raised concerns during his first term about the future of regional alliances. While no dramatic realignments have taken place, countries such as Japan, South Korea, and Taiwan appear increasingly aware of the need to prepare for potential shifts in the regional balance. Taiwan has focused on building resilience through stronger ties with the United States and efforts to diversify its economic relationships. Japan and South Korea, meanwhile, have continued to expand their regional diplomacy. In March 2025, for example, the foreign ministers of Japan, South Korea, and China met in Tokyo for the 11th Trilateral Foreign Ministers’ Meeting.²⁹ At the summit, the three countries agreed to promote "future-oriented cooperation," emphasizing areas such as economic integration, technological innovation, and supply chain resilience. They also committed to accelerating negotiations for a trilateral free trade agreement and deepening collaboration with ASEAN. Although the meeting centered on economic issues, it could signify something broader. With growing uncertainty around the future of U.S. involvement in the region, Japan and South Korea appear to be looking for more balance and flexibility in their foreign policies. The 2025 summit could suggest a quiet shift. While it doesn’t mark a break from the U.S.-led order, it suggests that regional powers are beginning to consider what it might mean to operate with more independence if American commitments become less predictable.

Notes

1. U.S. Department of Defense, "Defense Vision of the U.S.-ROK Alliance," News Release, November 13, 2023, https://www.defense.gov/News/Releases/Release/Article/3586528/defense-vision-of-the-us-rok-alliance/; Emma Chanlett-Avery and Mark E. Manyin, The U.S.-Japan Alliance, CRS In Focus, IF10199 (Washington, DC: Congressional Research Service, updated January 23, 2024), https://www.congress.gov/crs-product/IF10199.
2. Terri Moon Cronk, “U.S., South Korea Launch Annual Foal Eagle Exercise,” U.S. Department of Defense, March 3, 2017, https://www.defense.gov/News/News-Stories/Article/Article/1102331/us-south-korea-launch-annual-foal-eagle-exercise/; Danny Rangel, “U.S., Japan Successfully Conclude Joint Bilateral Exercise Keen Sword 25,” U.S. Indo-Pacific Command, November 1, 2024, https://www.pacom.mil/Media/News/News-Article-View/Article/3954464/us-japan-successfully-conclude-joint-bilateral-exercise-keen-sword-25/.
3. Edward Wong, “Trump Administration Approves F-16 Fighter Jet Sales to Taiwan,” New York Times, August 16, 2019, https://www.nytimes.com/2019/08/16/world/asia/taiwan-f16.html.
4. U.S.-China Economic and Security Review Commission, “China’s Response to U.S.-South Korean Missile Defense System Deployment and Its Implications,” July 26, 2017, https://www.uscc.gov/research/chinas-response-us-south-korean-missile-defense-system-deployment-and-its-implications.
5. Michael Flynn, Michael Allen, and Carla Machain, “Trump Wants South Korea and Japan to Pay More for Defense,” Washington Post, November 26, 2019, https://www.washingtonpost.com/politics/2019/11/26/trump-wants-south-korea-japan-pay-more-defense/.
6. Julian Borger, “US to Suspend Military Exercises with South Korea, Trump Says,” Guardian, June 12, 2018, https://www.theguardian.com/us-news/2018/jun/12/us-to-suspend-war-games-with-south-korea-donald-trump-kim-jong-un-north-summit.
7.  Masahiro Akiyama, “Redefining Self-Defense: The Abe Cabinet’s Interpretation of Article 9,” Tokyo Foundation, September 3, 2014, https://www.tokyofoundation.org/research/detail.php?id=536.
8. Tim Kelly and Sakura Murakami, “Pacifist Japan Unveils Biggest Military Build-up since World War Two,” Reuters, December 16, 2022, https://www.reuters.com/world/asia-pacific/pacifist-japan-unveils-unprecedented-320-bln-military-build-up-2022-12-16/.
9. “UK, Italy, Japan to Develop next-Generation Fighter Jet,” Defense Post, December 14, 2024, https://thedefensepost.com/2024/12/14/uk-italy-japan-joint-venture/.
10. Motoko Rich and Hisako Ueno, “Japan Relaxes Export Restrictions to Sell Patriot Missiles to U.S,” New York Times, December 22, 2023, https://www.nytimes.com/2023/12/22/world/asia/japan-export-patriot-missiles-us.html.
11. Ministry of Foreign Affairs of Japan, “Exchange of Diplomatic Notes for the Entry into Force of Japan-Australia Reciprocal Access Agreement,” accessed May 9, 2025, https://www.mofa.go.jp/press/release/press1e_000453.html; Ministry of Foreign Affairs of Japan, “Exchange of Diplomatic Notes for Entry into Force of Japan-UK Reciprocal Access Agreement,” accessed May 9, 2025, https://www.mofa.go.jp/press/release/press4e_003298.html; Ministry of Foreign Affairs of Japan, “Signing of the Japan-Philippines Reciprocal Access Agreement,” July 8, 2024, https://www.mofa.go.jp/s_sa/sea2/ph/pageite_000001_00432.html.
12. Ministry of Foreign Affairs of Japan, “Joint Statement Third Japan-India 2+2 Foreign and Defence Ministerial Meeting,” accessed May 9, 2025, https://www.mofa.go.jp/s_sa/sw/in/pageite_000001_00002.html.
13. Vannarith Chheang, “A Relationship Fit for the Times?” East Asia Forum, September 22, 2023, https://eastasiaforum.org/2023/09/22/a-relationship-fit-for-the-times/.
14. Prashanth Parameswaran, “What Does Moon’s ‘New Southern Policy’ Mean for ASEAN-South Korea Ties?” Diplomat, July 10, 2018, https://thediplomat.com/2018/07/what-does-moons-new-southern-policy-mean-for-asean-south-korea-ties/.
15. Clement Charpentreau, “South Korea’s Final KF-21 Prototype Completes First Flight: Video,” AeroTime, July 4, 2023, https://www.aerotime.aero/articles/south-korea-kf-21-fighter-final-prototype.
16. “South Korea’s New Missile Defense System Boosts Autonomy and Export Potential,” Korea Pro, December 2, 2024, https://koreapro.org/2024/12/south-koreas-new-missile-defense-system-boosts-autonomy-and-export-potential/?t=1746823297071.
17. Chris H. Park, “Is South Korea Ready to Be a Global Pivotal Arms Exporter?” Diplomat, July 13, 2023, https://thediplomat.com/2023/07/is-south-korea-ready-to-be-a-global-pivotal-arms-exporter/.
18. “Joint Statement on U.S.-ROK Guidelines for Nuclear Deterrence and Nuclear Operations on the Korean Peninsula,” U.S. Embassy & Consulate in the Republic of Korea, July 12, 2024, https://kr.usembassy.gov/071224-joint-statement-by-president-biden-and-president-yoon-on-u-s-rok-guidelines-for-nuclear-deterrence-and-nuclear-operations-on-the-korean-peninsula/.
19. “Fact Sheet: The Trilateral Leaders’ Summit at Camp David,” U.S. Embassy & Consulates in Japan, August 18, 2023, https://jp.usembassy.gov/fact-sheet-trilateral-summit-at-camp-david/.
20. John Dotson, “Taiwan Announces an Increased Defense Budget for 2024,” Global Taiwan Institute, September 21, 2023, https://globaltaiwan.org/2023/09/taiwan-announces-an-increased-defense-budget-for-2024/.
21. John Dotson, “Porcupine or Honey Badger?: The ‘Overall Defense Concept’ and Asymmetry in Taiwan’s Defense Strategy,” Global Taiwan Institute, May 17, 2023, https://globaltaiwan.org/2023/05/porcupine-or-honey-badger-the-overall-defense-concept-and-asymmetry-in-taiwans-defense-strategy/.
22. Yu-chieh Liu and Lery Hiciano, “Hai Kun to Undergo Sea Trials Soon, Source Says,” Taipei Times, May 9, 2025, https://www.taipeitimes.com/News/taiwan/archives/2025/05/10/2003836643.
23. Christine Casimiro, “Taiwan Receives First Batch of Harpoon Anti-Ship Missile Systems from the US,” Defense Post, October 2, 2024, https://thedefensepost.com/2024/10/02/taiwan-receives-harpoon-missile/.
24. Johnathan Harman, “Taiwan’s Missile Production Program: A Success Two Years Ahead of Schedule,” Global Taiwan Institute, October 30, 2024, https://globaltaiwan.org/2024/10/taiwans-missile-programs/.
25. U.S.-Taiwan Trade and Economic Relations, April 10, 2025, https://www.congress.gov/crs-product/IF10256.
26. Wendell Huang and Nina Kao, “TSMC Intends to Expand its Investment in the United States to US$165 Billion to Power the Future of AI,” Taiwan Semiconductor Manufacturing Company, March 4, 2025, https://pr.tsmc.com/english/news/3210.
27. Ibid.
28. “US Approves $385M Arms Sales to Taiwan,” Defense Post, November 30, 2024, https://thedefensepost.com/2024/11/30/us-taiwan-f-16/.
29. “The 11th China-Japan-ROK Trilateral Foreign Ministers’ Meeting Held in Tokyo,” Ministry of Foreign Affairs of the People’s Republic of China, March 22, 2025, https://www.fmprc.gov.cn/eng/wjbzhd/202503/t20250325_11581396.html.