This post is authored by John K. Warden, a U.S. defense and foreign policy analyst at the Institute for Defense Analyses. It is part of a project conducted by the program on U.S.-Korea policy at the Council on Foreign Relations, supported by the Smith Richardson Foundation and Korea Foundation. This series of posts addresses the U.S. nuclear posture in Northeast Asia, implications of North Korean nuclear and missile programs for U.S. extended deterrence commitments, operational and tactical dimensions of deterrence on the peninsula, and regional dimensions of stability. To further stimulate an open discussion of these issues, we would like to invite reader responses. Please contact Ellen Swicord at firstname.lastname@example.org for submission guidelines if you are interested in contributing a response
In both Europe and Northeast Asia, the growing threat of military aggression backed by nuclear threats is straining the credibility of U.S. alliance commitments. But while Europe is adapting within the framework of a multilateral alliance, Japan and South Korea are adjusting their deterrence strategy and posture in separate bilateral alliances with the United States. Promoting greater trilateral cooperation between the U.S.-Republic of Korea (ROK) and U.S.-Japan alliances would bring Northeast Asia closer to the North Atlantic model of collective defense, but doing so comes with significant risk.
There remains a possibility that negotiations will result in a cap on North Korea’s capabilities or, in the long run, the denuclearization of North Korea. But without a deal on the horizon, the United States and its allies must prepare for the possibility that they will have to deter and contain a nuclear-armed North Korea. If North Korea’s leader Kim Jong-un comes to think that he can threaten nuclear escalation to coerce the United States and its allies to accommodate his demands, then North Korea will likely be more willing to initiate provocations, escalate crises, and risk war.
Fortunately, the United States has strong alliances with South Korea and Japan, each undergirded by significant defense cooperation and integration. All three countries share concerns about China’s growing military might and regional influence and North Korea’s belligerence and growing nuclear capabilities. Moreover, both the U.S.-Japan and U.S.-ROK alliances have taken prudent steps to counter North Korea’s improving nuclear forces, such as deploying improved missile defenses.
But in contrast to Europe, U.S. bilateral alliances in Northeast Asia are not integrated into a multilateral security framework. The North Atlantic Treaty Organization (NATO) includes a political commitment to collective self-defense and an institutional mechanism for consensus decision-making, both of which are wholly absent between South Korea and Japan. NATO also has multilateral command arrangements and standards for interoperability that support a credible military posture.
In Northeast Asia, the United States has highly integrated military relationships with South Korea and Japan respectively, but there are no mechanisms to support trilateral military operations in a conflict. When threat perceptions were particularly high, Japan and South Korea were willing to modestly increase defense cooperation in areas such as intelligence sharing. But deeper partnership has been hamstrung by political clashes stemming from nationalism, economic and territorial disputes, and disparate interests. As a result, significant operational and tactical coordination and integration between Japan and South Korea remains out of reach.
From a deterrence perspective, there are advantages and disadvantages to greater multilateral integration. On the one hand, a multilateral deterrence strategy could be more credible to potential adversaries. Integrated allied military capabilities act as a force multiplier for the United States, making it easier to maintain credible deterrence of multiple adversaries in an increasingly multipolar world. Together, NATO allies can impose a much higher political, economic, and military cost on Russia than any one country plus the United States. If Russia is confident that an attack on one NATO ally will lead to a collective response, then it will likely calculate that the costs and risks of aggression are not worth the benefit.
But multilateral integration can also create a vulnerability that potential adversaries can exploit. At the political level, there are parallels between the challenge of coordinating between allies with different interests in Europe and Northeast Asia. While much of Europe is included in NATO, there are nonetheless divergent threat perceptions. Eastern European allies on Russia’s periphery, such as Lithuania, Latvia, Estonia, and Poland, worry that Russia might undermine their territorial integrity and yearn for greater military presence and stronger deterrence messaging. Allies in Central, Western, and Southern Europe, by contrast, face a less of a direct military threat from Russia and, as a result, many are less motivated to take steps to deter or respond to Russian aggression.
If Russia perceives that the defense of a NATO ally depends on a collective military response, it may see an opportunity to divide NATO in order to achieve its objectives. Russia might, for example, calculate that NATO’s consensus-based decision-making would be too slow, allowing it to achieve a military fait accompli. Russia might also see an opportunity to use nuclear threats against NATO allies that are supporting military operations to coerce them to back down. If NATO is perceived as being dependent on staging areas and rear-operating bases in Central and Western Europe, then Russia may see a path to victory by coercing certain allies to abandon the Baltic States.
The same theoretical benefits and risks to multilateral defense integration exist in Northeast Asia, but the benefits are less credible and the risks more pronounced. Like in Europe, North Korea would likely be deterred from attacking either South Korea or Japan if it expected an ironclad triumvirate to respond. But North Korea has a history of trying to drive wedges between South Korea, Japan, and the United States. At present, North Korea is attempting to divide via diplomacy. But in the future, it may attempt to advance its interests by conducting targeted aggression against either South Korea or Japan and coercing the other to remain out of the fray. Given the frailty of Japan-South Korea relations at even the best of times and the lack of an institutional mechanism to bind them, dividing South Korea and Japan will likely be a central component of North Korean strategy.
The likelihood that North Korea will see an opportunity to exploit divisions between the U.S-ROK and U.S.-Japan alliances will only grow as North Korea’s nuclear arsenal increases in size and sophistication. In the past, Japan could allow the United States to use its territory as a staging area and rear operating base for conflict on the Korean Peninsula with limited risk. But now, facing a credible nuclear threat, the potential cost to Japan of supporting U.S. military operations on the Korean Peninsula is much higher, and will continue to grow.
This is the essential dilemma of trilateralism in Northeast Asia. Greater trilateral integration of U.S., Japanese, and ROK military planning and operations has the potential to enhance conventional deterrence. If Japan and South Korea strengthen cooperation on air and missile defense and anti-submarine warfare, they would meaningfully improve their collective military capability. But to the extent that increasing integration leads to operational dependency, trilateralism could be counterproductive. North Korea may see operational integration as a seam that it can attempt rip.
Until South Korea and Japan fundamentally transform their political relationship, there is no obvious way to avoid this dilemma. The United States should, however, carefully consider the benefits and risks before taking steps that would increase dependencies between the U.S.-ROK and U.S.-Japan alliances.