Extended Nuclear Deterrence: Threats and Challenges to U.S. Alliance System in Northeast Asia

Since the Cold War and the demise of the Soviet Union in 1991, the United States has successfully managed to protect its alliance system in Northeast Asia, consisting of Japan and South Korea, against external threats from adversaries by offering extended nuclear deterrence to these countries.

However, the new geopolitical landscape that has emerged over the past few years with the rapprochement between the anti-U.S. front at regional and international levels and the rapid modernization of these countries’ nuclear arsenals has led to re-questioning the credibility of Extended Nuclear Deterrence among the allies. At the same time, Russia’s attempt to change the status quo by force in the Ukraine War, China’s intensified activities around Taiwan, and North Korea’s new law consecrating the right to carry out nuclear strikes to destroy threats have all further exacerbated the situation. Furthermore, the rising regional arms race, rapid change of regional and international nuclear arms posture, and the strengthening of nuclear forces both in quantity and quality have led Japan and South Korea to increase their defense budget substantially.

The nature of the growing threat from multi-directions increasingly deteriorates the technical adequacy of extended nuclear deterrence. This is especially relevant in the face of the rising threat from North Korea on the one hand and the Chinese expansionism toward Japan and Taiwan on the other.

Changing Regional Geopolitical Landscape

The imminent threat to the United States and its allies is a sudden nuclear attack that will come from North Korea. As no negotiations and agreements with North Korea have yielded results so far, Pyongyang continues to expand and enrich its nuclear arsenal in quality and quantity. A Rand Corporation analysis suggests that by 2027, North Korea “could have 200 nuclear weapons, several dozen intercontinental ballistic missiles (ICBMs), and hundreds of theater missiles for delivering the nuclear weapons.” Reaching such capacity in nuclear warheads and delivery systems will significantly raise the Democratic People’s Republic of Korea’s (DPRK) position to that of a regional nuclear power. In addition, with the increased range and sophistication of weapon development, the number of ballistic missiles launched by the DPRK has already reached 33 in 2022.

The geographical proximity between the two Koreas increases the concerns of the southern part of the peninsula. The level of anxiety is strikingly reflected in the results of surveys conducted in Seoul and other major cities of South Korea. Despite accelerated developments in the defense industry since the Moon Jae-in administration and Seoul’s superiority in conventional warfare capability, the absence of MAD (mutual assurance destruction) against an adversary whose nuclear power capability is dramatically growing complicates the present geopolitical landscape for Seoul. The current countermeasures strategies designed by Seoul, comprising of Kill-Chain, Korea Air Missile Defense (KAMD) and Korea Massive Punishment and Retaliation (KMPR), will not be fully functional in deterring a sudden nuclear attack from Pyongyang due to time constraints and locating the launched missiles.

Moreover, the nuclear umbrella provided by the U.S. to South Korea was in a period when North Korea did not yet have intercontinental ballistic missiles and tactical nuclear weapons.  Much has changed since, including the rapid modernization of the North Korean arsenal. Pyongyang left the NPT, developed WMD capability, and achieved the capacity to strike the U.S. mainland with its ICBMs. Aside from that, the North has also developed Hypersonic Glide Vehicles (HGV), which have the potential to easily infiltrate and target the South’s defense systems. All these evolvements raise the question of whether the present extended deterrence would be capable of protecting the allied country from a nuclear-capable adversary.

Issues such as burden-sharing and troop withdrawal threats against allied nations during the Trump administration, combined with the question of to what extent will the United States protect allies at the expense of endangering U.S. cities in the event of a nuclear attack, have all increased the demand for nuclear weapon acquisition in public and elite levels dramatically. A poll conducted by The Chicago Council on Global Affairs showed that 71 percent of South Korean respondents supported developing an indigenous nuclear weapons program, while 56 percent supported the deployment of U.S. nuclear weapons in South Korea to deter a possible nuclear attack from North Korea. When asked to choose between domestic nuclear weapons and U.S. deployment, 67 percent prefer an independent arsenal over U.S. deployment (9 percent).

China’s Rising Nuclear Capability and Russian War in Ukraine

The second rising asymmetrical challenge to the U.S. extended deterrence and its allies’ national security is China’s rising military power projection and rapid modernization of its silo-based long-range nuclear missiles. Beijing’s construction of new long-range missile silos and rapid nuclear buildup has raised alarm bells in Seoul, Tokyo, and Washington. According to a US Defense Department Report released in 2021, China’s nuclear expansion may enable it to have up to 700 deliverable nuclear warheads by 2027. China likely intends to have at least 1,000 warheads by 2030. Beijing is further establishing nuclear interoperability by developing a nuclear-capable air-launched ballistic missile (ALBM) and improving its ground and sea-based nuclear capabilities.

Combining Beijing’s growing nuclear power capability with its efforts to change the security architecture around the East and South China Seas and the intensified military pressure around Taiwan has led Washington to create multidimensional and comprehensive strategies with regional allies to counter the rising threat. Japan and the U.S. recently agreed on joint technological research to counter hypersonic weapons to deal with China’s intensified military activities around Japan following China’s launch of ballistic missiles as part of large-scale exercises around the Taiwan Strait during Speaker Nancy Pelosi’s visit in August 2022. However, it remains unclear whether Japan and South Korea’s security efforts are fully secure against the ever-increasing nuclear threats posed by China and North Korea.

The Russian invasion of Ukraine has fueled security concerns in both Japan and South Korea. Japan has an unresolved dispute with Russia over the Kuril Islands and with China in the East China Sea over the Senkaku/Diaoyu Islands while South Korea faces an imminent nuclear threat from North Korea. The rising threat environment in East Asia has led to a rapid increase in defense expenditures and capacity in both South Korea and Japan. This is more marked in the case of Japan as it has been subject to a pacifist constitution for years and is highly opposed to nuclear weapons due to its nuclear experience in Hiroshima and Nagasaki. Now, Japan has been working on a new defense policy, including bolstering its ability to strike enemy bases and sharing tactical nuclear weapons with the United States.

Additionally, the idea that Ukraine is open to Russian invasion because it has abandoned its nuclear weapons causes the allied countries to pressure their governments to acquire nuclear weapons, whether independent or U.S. deployment.  Furthermore, one of the severe concerns that emerged in East Asia after Russia’s invasion of Ukraine is that Moscow succeeded in annexing and settling the eastern regions of Ukraine while being able to demonstrate its capability to pass its Far East battleships near the Japanese archipelago for the long mission, although it has been severely weakened economically, militarily, and diplomatically by sanctions. The situation brought along the concerns of Japan and South Korea, both at public and decision-makers level, about to what extent the US, which also is struggling with Pyongyang and Beijing, can defend themselves in real wartime. Thus, Russia’s invasion of Ukraine has brought the US to the third nuclear front, dividing its effort, and distracting its focus from East Asia while simultaneously causing Japan and South Korea to question nuclear options.

Nuclearization of Allies to Keep U.S. Alliance System Sustainable?

In a situation where a nuclear triad consisting of Russia, China, and North Korea increases its interoperability in East Asia and the Pacific Region, Japan and South Korea will have no chance to counter a threat even if they are protected by extended nuclear deterrence. In the worst scenario, the Chinese invasion of Taiwan is seen as an opportunity by North Korea to launch a simultaneous attack on the South placing heavy burdens on the U.S. and its allies to avoid facing irreversible damage. Current developments in China’s anti-access/area denial (A2/AD) capability and North Korea’s missile inventory put at risk critical U.S. and allied forces assets in Northeast Asia that could respond to regional contingencies. Moreover, China and North Korea’s geographical advantages as well as their growing nuclear arsenal and development expertise place them favorably to contend with the U.S. in the multi-domain, implying a distinctive military advantage.

The altered geopolitical landscape along with the strengthening ideological and practical rapprochement between Russia, China, and North Korea raise doubts about the U.S.’s commitment to extended nuclear deterrence. The efforts to reduce the role of nuclear weapons seem to only bind U.S. allies while Russia, China, and even North Korea continue to modernize and extend their nuclear arsenals. Changing regional balances of power and significantly lowering the threshold of nuclear war may leave the U.S. with the sole option of allowing or even supporting its two critical allies in Northeast Asia to acquire and produce nuclear weapons to secure and maintain their regional alliance system.

The emerging new nuclear geopolitical landscape in Northeast Asia has the potential to lead to distrust in credibility and commitment between the United States and its allies over time. Further, adversaries’ nuclear position could cause U.S. allies to demand more nuclear assurance through their independent arsenal or U.S. nuclear-sharing programs similar to AUKUS. The looming nuclear triad from Northeast Asia is a critical threshold and testing ground for U.S. global supremacy. Providing guarantees to its allies in every aspect and maintaining its leadership will be achieved only by a collaborative approach to eliminate the triad threat which cannot be underestimated by any political or military means.


The coming to power of Yoon Suk Yeol, who is inclined to cooperate closely with Japan in South Korea, further facilitated the implementation of economic, diplomatic, and military interoperability processes between Washington’s two critical allies in northeast Asia. Several issues were focused on, such as the reassessment of technical issues related to expanded deterrence between the parties and the reassessment of the security of Seoul, which felt imminent threats, and the deficiencies in its defense systems. However, despite all joint efforts, the three nuclear powers, which were already close ideologically, began to converge their effort in the military and technological fields following the invasion of Ukraine. Meanwhile, the hypersonic arsenals that this triad has can easily penetrate the defense systems of the allies while the nuclear guarantor of extended deterrence, Washington, has been preoccupied with several fronts simultaneously, leaving the US allies in northeast Asia vulnerable in the face of rising new geopolitical threat environment.

The necessity to further reduce the Allies’ dependence on the United States, enabling them in a position to defend themselves independently, and thus maintaining the existing alliance system in northeast Asia, could leave Washington with the choice of providing the Allies with tactical nuclear weapons or allowing them to produce their own domestic nuclear weapons.