The most feasible way for Japan and South Korea to achieve security independent of the United States is to strengthen their relationship, ultimately moving toward a formal alliance. An unspoken motivation behind the push by Japanese Prime Minister Ishiba Shigeru for an ‘Asian NATO’ may indeed be developing a security relationship with South Korea. For both countries, attaining true security independence is the only way to mitigate the security dilemma posed by their military reliance on the United States, especially given growing concerns over rising U.S. isolationism.
Ishiba’s extensive experience in national defense shapes his realistic worldview. Therefore, his primary motivation for pursuing security independence is to safeguard Japan’s geopolitical interests amid growing threats from China, North Korea, and Russia. This strategy is particularly timely, given rising uncertainties about U.S. commitment to Japan’s defense. And Ishiba’s proposal to station Japan’s Self-Defense Forces (SDF) in Guam could be a feasible step toward enhancing Japan’s military maneuverability.
Despite his ambition, Ishiba understands that a completely militarily independent Japan through an ‘Asian NATO’ cannot be built overnight. Nevertheless, his concept of collective security in Asia signals a long-term strategy, with South Korea emerging as Japan’s most viable regional ally. The signal was warmly received by South Korea. In his first phone call with Ishiba, South Korean President Yoon Suk Yeol expressed support for stronger security ties with Japan, emphasizing shared values and geopolitical interests: Both democratic nations face threats from North Korea, whose advancing nuclear capabilities are a growing concern. Compounding the threat is North Korea’s recent military technology transfer from Russia and deeper cooperation with China, which have escalated regional tensions.
Although both Tokyo and Seoul currently rely on Washington for defense, their geographical proximity makes them each other’s most immediate partners in the event of a regional security crisis. South Korea’s Three Axis system, which includes missile defense and counterstrike capabilities, is geopolitically more critical for Japan’s defense against regional threats than the uncertain level of U.S. assistance. Strengthening bilateral defense cooperation between Seoul and Tokyo is therefore a strategically logical move for both nations.
However, Japan’s pursuit of tighter security ties with South Korea does not necessarily mean the exclusion of the United States. The underlying motivation for both countries seeking greater security independence from their primary security guarantor stems from the security dilemma created by extensive American involvement in the Asia-Pacific region. For South Korea, the asymmetric nature of its alliance with the U.S. has limited its leverage. Washington has historically restricted South Korea’s access to advanced military technologies, while also pressuring Seoul to pay more for the alliance. This has increased South Korea’s military burden and complicated its relations with North Korea, driving Seoul to cautiously pursue greater security autonomy.
Japan faces a similarly complex dilemma. While South Korea must always be prepared for a potential conflict with North Korea, Japan has choices. If war breaks out in the Taiwan Strait, the U.S. would need Japan’s permission to use its military bases to deploy forces in defense of Taiwan. This places Japan in a difficult position: agreeing risks Chinese retaliation, while refusal could undermine the U.S.-Japan alliance, Japan’s primary security guarantee.
For Japan, the fundamental goal of military build-up is to enhance deterrence and self-defense, not to provoke conflict. Although strong ties with the U.S. provide security assurances, they may also limit Japan’s autonomy in making critical security decisions. Therefore, Japan has every reason to pursue security independence, much like South Korea. Yet given the limited military capacities of both nations, achieving full security independence individually is impractical. The most feasible path forward is through closer cooperation with each other.
However, a closer alliance between Japan and South Korea could push them toward prioritizing East Asia’s interests, which would, in essence, challenge U.S. power projection in the Asia-Pacific region. It is therefore unsurprising that Washington does not fully share Ishiba’s enthusiasm for an ‘Asian NATO’. U.S. Assistant Secretary of State Daniel Kritenbrink expressed skepticism, stating that it is “too early to talk about collective security in that context” and emphasizing that the U.S. is focused on “investing in the region’s existing formal architecture” and strengthening informal relationships. But does the current U.S.-led regional framework truly enhance security for Japan and South Korea?
The answer is no. While U.S.-Japan and U.S.-ROK security treaties formalize their alliances with America, their ties to other U.S. allies in Asia – such as the Philippines and Indonesia – remain quasi-alliances at best. In practice, the U.S. has significant influence over these countries’ decisions to provide military assistance should Japan or South Korea face a security threat. As a result, Tokyo and Seoul must constantly prove themselves as credible allies to Washington to ensure future support.
A recent example is Japan and South Korea’s substantial economic and military aid to Ukraine, aimed at strengthening ties with the U.S.-led NATO. However, this move risks inflaming fears of encirclement in China and North Korea, further escalating regional tensions. Moreover, it stretches both countries’ military resources, potentially undermining their own defense build-up. By aligning too closely with U.S. and European interests, both Tokyo and Seoul risk losing the flexibility to manage their own security and economic priorities.
As the United States remains entangled in regional conflicts such as those in Ukraine and Gaza, its influence in Asia is inevitably declining, providing an opportunity for middle powers like Japan and South Korea to reassess their defense strategies in an increasingly complex geopolitical landscape. While unresolved historical disputes may temporarily hinder closer security cooperation between the two nations, the growing security threats in the region dictate that a stronger Japan-South Korea relationship is the most viable path to ensuring both nations’ security while gradually achieving greater autonomy from America.
