An Alliance Division of Labor in East Asia


Leaders in Washington understand that a strategy for the Indo-Pacific rooted in alliances is critical to meet the challenge presented by China. But such a strategy seems slow in coming together in East Asia. Why is this the case?

Two years ago, we argued that the fundamental reason for the lack of security cooperation between Japan and Korea is their diverging geopolitical orientations. Yet the situation has changed in recent years. President Joe Biden met with the leaders of Japan and South Korea on the sidelines of the NATO Summit in Madrid to discuss greater security cooperation. The new South Korean president, Yoon Suk-yeol, declared a shift in foreign policy, moving Seoul even closer to Washington and even to Tokyo, with which it shares a difficult history. Underlying the policy shift of the new leadership are structural changes that make the two countries’ interests compatible in the long run, presenting a real opportunity to further trilateral security cooperation.



How can policymakers on both sides of the Pacific seize this opportunity to overcome the challenges and forge closer security ties among U.S. allies in this region? By conceptualizing alliances as a division of labor, policymakers can specify ways that respective allied members contribute to the common defense.

From “Hub-and-Spokes” to a “Network-Based” Alliance System

Alliances are commonly conceived of as a way to maintain the balance of power or simply as a means of “capability-aggregation.” This parsimonious understanding of alliances may leave the impression that strengthening collaboration among U.S. allies is a straightforward endeavor. However, such an approach does not, by itself, explain the absence of a NATO-like multilateral alliance structure in the western Pacific.

In East Asia, the U.S. alliance system developed into a peculiar structure due to geography — often referred to as the “hub-and-spokes” system based on a collection of bilateral alliances. Hindered by the large bodies of water separating them, U.S. allies in the region have divergent threat perceptions and geopolitical orientations. For instance, Japan has benefited from its insular position and U.S. naval primacy, providing it with strategic immunity. Tokyo, therefore, has not only focused on economic development while deemphasizing the role of military power, but also sought to avoid entanglement in regional security affairs by pursuing a bilateral alliance with the United States. In contrast, South Korea and Taiwan were Cold War hotspots, and the United States preferred a bilateral arrangement designed to restrain and control them from taking adventurous action.

Since the Obama administration, Washington has sought to transform the “hub-and-spokes” system into a network-based model, enhancing the role of alliances by encouraging additional burden-sharing and closer security coordination among U.S. allies. One notable example of this effort is the signing of an intelligence-sharing agreement between Seoul and Tokyo in November 2016. Yet, there is a disconnect between rhetoric and action, and these initiatives to bolster security relations among U.S. allies have not made much progress since then.

A key reason for this gap is divergent strategic priorities among U.S. allies. As Paul Poast argues, the success of alliance negotiation depends in large part on the agreement over joint war plans. Although Japan, South Korea, and the United States all face shared threats from North Korea and China, they prioritize them in different ways, thereby making it difficult to forge a joint war plan. One way to overcome this challenge is to devise a framework that clarifies their division of labor, based on their different strategic positions, to coordinate and aggregate these allies’ different capabilities in countering China’s revisionism in the Indo-Pacific.

The Regional Response

While progress on transforming the regional alliance network remains sluggish, U.S. allies in the western Pacific have been making important changes to their strategic posture in the 2010s in response to the changing regional environment. Japan, for instance, started to integrate military power into its overall national strategy, a change from its postwar habit of buck-passing its security to the United States. However, as China’s maritime expansion started jeopardizing Tokyo’s independence as a maritime state, Japan is shifting its geostrategic focus from the north — namely Russia — which had been the main concern during the Cold War, to the south. Concurrently, Japan initiated several national security reforms in the 2010s — both legal and institutional — to elevate the role of military power in its national strategy, paving the way for closer security cooperation with the United States. Chief among them: unshackling the self-imposed legal restraints on the use of military force, especially on exercising the right to collective self-defense, was crucial for the two allies to further develop a closely integrated joint war plan. In this context, the United States and Japan have been upgrading their security cooperation in the Indo-Pacific, resulting in the 2015 U.S.-Japan Defense Cooperation Guidelines, which strengthened the alliance coordination mechanism and enhanced operational coordination.

Although long unconcerned about the China challenge due to its “hybrid” position between land and sea, several factors are leading South Korea to reconsider its posture. First, in recent years, the Korean public has grown wary of China’s increasingly aggressive behavior. This tendency is more pronounced among younger generations. According to a 2021 poll, Koreans in their 20s and 30s tend to perceive China as a bigger threat than North Korea. Relatedly, the country’s demographic shrinkage will require it to focus on capital-intensive capabilities, including air and naval forces, instead of fielding a large army. Further investments in air and naval capabilities can provoke a reaction from Beijing, regardless of Seoul’s intentions. Finally, strategic and political changes have led some analysts to argue that Korea should rethink its erstwhile military strategy predicated upon total war to achieve unification. A new strategy, they argue, should focus instead on limited war to prevent Pyongyang’s use of nuclear weapons and Beijing’s intervention. In short, China is increasingly looming large in the minds of policymakers in Seoul.

Division of Labor and U.S. Alliance Strategy in East Asia

One of the main objectives of U.S. strategy in managing great power rivalry in East Asia involves preventing China’s expansion outside the first island chain while imposing costs to selectively temper its growth and distract investments away from offensive capabilities. While Japan and South Korea have responded to the challenges imposed by China’s increased assertiveness, the question is how the United States can coordinate these efforts for the common defense. In other words, what is the ideal division of labor? Among many factors at play, geography is the first cut. Two geographic areas are of particular interest to the regional balance of power: Taiwan and the Korean peninsula.

The main task for the United States and Japan is to focus on sea control amid a widening Sino-Japanese naval imbalance. Mounting concerns over eroding naval advantages have resulted in Japan closely aligning with the United States, the dominant naval power, through tighter alliance coordination. From Washington’s perspective, the defense of the first island chain — particularly the Japanese archipelago — has been considered crucial as “a strong outpost” for power projection in the western Pacific. On the other hand, for Tokyo, the freedom of navigation of its surrounding waters is crucial in preserving its independence and prosperity as a trading nation.

Japan has, therefore, increasingly embraced its role as a maritime state by investing in its naval capabilities as it enhances its contribution to the common defense. The East China Sea, where the Senkaku/Diaoyu Islands are located, plays a central role in Sino-Japanese maritime competition and the overall naval balance of power. Japan’s Maritime Self Defense Force has unique advantages in intelligence, surveillance and reconnaissance capabilities, anti-submarine warfare, and the overall defense of the sea lines of communication in these waters. Moreover, the importance of sea control for Japan’s security and the U.S.-Japanese alliance suggests that the defense of Taiwan could be one of the key priorities for the alliance given the geopolitical consequences of China’s potential conquest of the island. China’s military drills following U.S. House Speaker Nancy Pelosi’s visit to Taiwan — during which five missiles landed in Japan’s exclusive economic zone — reinforced the view in Tokyo that the island nation would not be spared during a Taiwan “contingency.” Yet, Japan’s contribution still faces some limitations, especially in a potential conflict over Taiwan. In particular, despite a series of security reforms in the 2010s, some legal hurdles remain for Japan to authorize the use of force by the Self Defense Forces to support the U.S. militarily in a future regional conflict.

South Korea’s position is slightly more delicate: it faces North Korea as an immediate threat and China as a looming challenge. Specifically, the latter poses both immediate problems, such as illegal fishing in territorial waters and arbitrary intrusion into Korea’s air defense identification zone, as well as the distant-yet-graver possibility of intervention should North Korea collapse. Moreover, Seoul’s deep economic ties with Beijing will likely prevent it from hard balancing, at least in the short run. Yet, the Korean peninsula is the only place on the Asian continent where the United States stations troops to maintain an advantageous position. Washington’s task, then, is to help Seoul to capitalize on existing resources to deter North Korea and impose costs, albeit indirectly, on China, while realigning the two countries’ means and ends.

These measures include encouraging and aiding Seoul’s development of a network of intelligence surveillance, and reconnaissance assets along its western and southern islets, the unmanned combat aerial vehicles program to reconnoiter its Air Defense Identification Zone, investments in air/missile defense and cyber capabilities against North Korea and China, and proactive participation in joint military exercises outside of the peninsula. Specifically, the South Korean Marine Corps is the second largest in the world — a byproduct of its geography and strategic history — and therefore can play a larger role in regional security cooperation. Its potential participation in the KAMANDAG exercise later this year will improve interoperability among U.S. allies and signal unity, thereby creating uncertainty for Chinese strategists. If better equipped, the Republic of Korea Marine Corps can also serve as an asymmetric deterrent against potential Chinese aggression. On Taiwan, Seoul will have limited bandwidth at this point, especially given its undecided naval policy exemplified in the debate over whether the country should acquire aircraft carrier. With time, however, its shifting geopolitical orientation will likely incentivize it to partake in any cross-strait crisis in some capacity.

Further, Washington can work with both Tokyo and Seoul simultaneously on two urgent tasks. The first is the normalization of the General Security of Military Information Agreement. It exemplifies how allies can complement their respective comparative advantages: Japan contributing advanced intelligence, surveillance, and reconnaissance assets; Korea contributing human intelligence and geographic proximity. This would require Washington to dissuade both countries from making provocative moves on politically sensitive issues involving territories and historical interpretations. Second, the United States should reaffirm its commitment to extended deterrence to prevent the rise of nuclear advocates in Seoul and Tokyo, encouraging instead a focus on defensive capabilities. Nuclear armaments — either in the form of independent nuclear arsenals or nuclear-sharing — is not only unhelpful in the case of Korea, but also counterproductive in the case of Japan. One would do well to recall that the possibility of Germany’s possession of nuclear weapons led Moscow to resort to brinkmanship, culminating in the Cuban Missile Crisis.

The Hurdles for an Enhanced Trilateral Security Coordination

The main challenges to closer security ties between Seoul and Tokyo can be attributed to structural factors such as diverging strategic priorities. Nevertheless, questions over agency remain. Tokyo’s security reforms in the 2010s were driven by structural factors — namely China’s maritime expansion — yet it is undeniable that the late former Prime Minister Shinzo Abe’s political acumen played a certain role in the successful implementation of these controversial reforms.

By the same token, a weak political foundation may inhibit the Yoon administration’s ability to improve its relations with Tokyo — the administration may be easily distracted by domestic politics and the many thorny issues that remain between the two Asian neighbors. The administration’s dwindling approval ratings may inhibit President Yoon from significantly upgrading security ties with its maritime partners — particularly with Japan. Indeed, the grievances rising from Japan’s imperial past that remain in South Korea have made managing relations with its neighbor a contentious issue. Some observers also suggest that the Korean public does not feel the urgency to fix the relationship with Japan. Most notably, the question of the liquidation of Japanese corporate assets in Korea pursuant to the Supreme Court decision of 2018 over the wartime labor issue has been a major concern for policymakers in both countries as it may derail the bilateral relationship. It could be challenging to reach some sort of grand bargain between Seoul and Tokyo. Washington may, therefore, be required to “manage” these differences and focus on practical defense and intelligence cooperation on a case-by-case basis, while having a broader strategic picture in mind.

The Path Forward 

Intellectual debates on American grand strategy often treat alliance commitments as a dichotomous choice — particularly between deep-engagers and restrainers. The question over the numerical costs and benefits of those commitments has attracted attention as great power rivalry once again becomes a salient feature of international politics. However, the question that deserves attention is how the United States could effectively operationalize its alliance system by integrating it into Washington’s overall grand strategy. The Anglo-American division of labor proved to be a theory of victory during World War 2, underscoring “how grand strategy is formed collaboratively” among allies. In a similar vein, a grand strategy that generates a common purpose among allies is vital. Conceptualizing alliance politics as a “division of labor” is an enabler that could further strengthen the trilateral security relationship among the United States, Japan, and South Korea by acknowledging and bridging their different strategic priorities.



Takuya Matsuda holds a Ph.D. in war studies from King’s College London where his research focused on alliance politics. This article was prepared while he was a non-resident Hans J. Morgenthau Fellow at the Notre Dame International Security Center and a visiting scholar at the Institute for Security and Conflict Studies at George Washington University.

Jaehan Park is a postdoctoral scholar at the Edwin O. Reischauer Center for East Asian Studies at the Johns Hopkins School of Advanced International Studies and a non-resident Hans J. Morgenthau Fellow at the Notre Dame International Security Center. He wishes to thank Richard Seongwon Lee for his thoughtful comments in preparing this article.

Image: Official Japan Maritime Self-Defense Force photo