Perspective – Inside the Japan-South Korea Alliance Less Trustful to the US

The most likely way for Japan and South Korea to find security outside the United States is to strengthen their relationship, eventually moving toward a formal alliance. The unspoken motivation behind Japanese Prime Minister Ishiba Shigeru’s ‘NATO for Asia’ campaign may indeed be improving security ties with South Korea. For both countries, achieving true security independence is the only way to reduce the security problem caused by their military dependence on the United States, especially considering the growing concern about the rise of US isolation.

Ishiba’s extensive experience in defense shapes his practical worldview. Therefore, his primary motivation for pursuing security independence is to protect Japan’s national interests amid growing threats from China, North Korea, and Russia. This strategy is especially timely, given the growing uncertainty about the US’s commitment to Japan’s defense. And Ishiba’s proposal to station Japan’s Self-Defense Forces (SDF) in Guam would be a possible step in developing Japan’s military power.

Despite his desire, Ishiba understands that a completely independent Japan through the use of ‘Asian NATO’ cannot be built overnight. Still, his concept of joint security in Asia reflects a long-term strategy, with South Korea emerging as Japan’s most active regional partner. The gesture was warmly received by South Korea. In his first phone call with Ishiba, South Korean President Yoon Suk Yeol expressed his support for a strong security relationship with Japan, emphasizing shared values ​​and the interests of the political world: Both of these democratic countries face threats from North Korea, whose nuclear capabilities are a growing concern. Adding to the threat is North Korea’s recent transfer of military technology from Russia and deepening cooperation with China, which has increased regional tensions.

Although both Tokyo and Seoul currently rely on Washington for security, their geographic proximity makes them the closest partners in the event of a regional security crisis. South Korea’s Three Axis system, which includes anti-missile and anti-missile capabilities, is more important geopolitically to protect Japan from regional threats than the uncertain level of US aid. Strengthening defense cooperation between Seoul and Tokyo is therefore a logical step for both nations.

However, Japan’s pursuit of a strong security relationship with South Korea does not mean that the United States will be excluded. The underlying motivation for both countries seeking greater security independence from their primary security provider stems from the security crisis created by America’s extensive involvement in the Asia-Pacific region. For South Korea, the asymmetric nature of its alliance with the US has limited its power. Washington has historically restricted South Korea’s access to advanced military technology, while pressuring Seoul to pay more for the alliance. This has increased South Korea’s military burden and strained its relationship with North Korea, prompting Seoul to cautiously pursue greater security independence.

Japan faces a similarly complex problem. While South Korea must always prepare for a potential conflict with North Korea, Japan has options. If war broke out in the Taiwan Strait, the US would need Japan’s permission to use its military bases to send troops to defend Taiwan. This puts Japan in a difficult position: acquiescence risks Chinese retaliation, while refusal could undermine the US-Japan alliance, Japan’s main security guarantor.

In Japan, the main goal of building up the military is to improve deterrence and defense, not to provoke conflict. While a strong relationship with the US provides security guarantees, it may also limit Japan’s independence in making key security decisions. Therefore, Japan has good reasons to pursue security independence, like South Korea. However, given the limited military power of both nations, achieving full mutual security freedom is not possible. The most likely way forward is closer cooperation.

However, the close relationship between Japan and South Korea may make them prioritize the interests of East Asia, which may, in fact, be a challenge to the US power projection in the Asia-Pacific region. It is therefore not surprising that Washington does not fully share Ishiba’s enthusiasm for an ‘Asian NATO’. US Assistant Secretary of State Daniel Kritenbrink expressed doubts, saying “it is too early to talk about collective security in that context” and stressing that the US is focused on “investing in the existing legal structure of the region” and strengthening informal relations. But does the current US-led regional framework really improve the security of Japan and South Korea?

The answer is no. While the US-Japan and US-ROK security agreements formalize their alliances with America, their commitments to other US allies in Asia – such as the Philippines and Indonesia – remain best alliances. In fact, the US has a lot of influence on these countries’ decisions to provide military aid if Japan or South Korea face a security threat. As a result, Tokyo and Seoul must always prove themselves as reliable friends to Washington in order to ensure future support.

A recent example is Japan and South Korea’s massive economic and military aid to Ukraine, aimed at strengthening relations with the US-led NATO. However, the move risks fueling fears of a spiral in China and North Korea, fueling regional tensions. In addition, it stretches the military resources of both countries, which may harm their defense structures. By aligning too closely with US and European interests, both Tokyo and Seoul risk losing the flexibility to manage their security and economic priorities.

As the United States remains mired in regional conflicts such as those in Ukraine and Gaza, its influence in Asia is inevitably waning, providing an opportunity for central powers such as Japan and South Korea to reassess their defense strategies in an increasingly political environment. Although unresolved historical disputes may hinder close security cooperation between the two nations, the increasing security threats in the region indicate that a strong relationship between Japan and South Korea is the most effective way to ensure the security of both nations while gradually gaining greater independence from America.

Further Studies in E-International Relations