Deepening Regional Security Dilemma Amid North Korea’s Enhanced Tactical Nuclear Doctrine and Trilateral Arms Buildup

Executive Summary

Based on its doctrine of preemptive use of tactical nuclear weapons, established at the 8th Party Congress in 2021, North Korea is pursuing a dual-track strategy. It maintains a hardline stance toward South Korea, framing Seoul’s acquisition of nuclear-powered submarines and Tokyo’s defense spending increase as a “nuclear domino effect” and “remilitarization,” respectively, while simultaneously keeping a separate channel open to the United States in response to conciliatory signals from the Trump administration. Japan, under the Takaichi administration, has requested an increased defense budget of 8.8908 trillion yen for fiscal year 2027 and is set to announce a new Medium Term Defense Program this year, a move justified by a dual deterrence logic aimed at countering threats from North Korea and China's maritime expansion. China criticizes Japan's military expansion as a return to militarism, effectively aligning with North Korea's anti-Japan framing, a trend that is increasingly subordinating the Korean Peninsula issue to the broader U.S.-China rivalry. The most likely scenario is a continuation of the status quo, where North Korea maintains its dual strategy toward the U.S. and South Korea, while trilateral military exercises, Japan’s defense buildup, and South Korea’s nuclear submarine project proceed at their own pace. However, if these three triggers cross a critical threshold simultaneously, the risk of escalation could become tangible. South Korea needs to manage the security rationale and non-proliferation narrative for its Jangbogo-N project in parallel, without undermining extended deterrence consultative mechanisms. It also needs to secure prior consultation channels to prepare for potential shifts in U.S. channels of communication with North Korea.

I. Issue Analysis

Issue Analysis: North Korea's Enhanced Tactical Nuclear Doctrine and the Regional Arms Race

1. Background and Developments

The ostensible trigger for the current situation was an internal U.S. Department of Defense discussion on a new nuclear strategy. However, Pyongyang's reaction is not an isolated event. It is rooted in the doctrine of preemptive use of tactical nuclear weapons, which has been in place since the 8th Party Congress in 2021 [3]. Starting in early August 2026, North Korea's foreign ministry and state-run media have issued a series of external statements.

On August 12, First Vice Foreign Minister Jang Kum Chol described South Korea's plan to acquire "Jangbogo-N" nuclear-powered submarines as a "new risk factor for security in the Asia-Pacific region" [3]. North Korea warned that this project could trigger a regional "nuclear domino effect" [3]. Two days later, a military commentary criticizing the new U.S. nuclear strategy was published simultaneously in the Korean Central News Agency and Rodong Sinmun [6]. Around the same time, a foreign ministry spokesperson issued a separate statement ahead of the start of joint ROK-U.S. military exercises [6].

Developments in Japan are intertwined with these events. On August 31, Japan's Ministry of Defense requested a budget of 8.8908 trillion yen (approximately 76.3 trillion won) for fiscal year 2027, an increase of 80 billion yen from the previous year [18]. Prime Minister Takaichi is scheduled to announce a new Medium Term Defense Program within the year [16]. The budget request includes the development of submarine-launched hypersonic missiles, research to equip unmanned submersibles with long-range missile launch capabilities, and the development of long-range attack drones [1][16]. North Korea's Rodong Sinmun criticized this, stating that "Japan's expansion of its defense industry will only increase crises" and calling it a "military budget proposal aimed at further enhancing the war-fighting capabilities of the Self-Defense Forces" [1].

2. Current Situation

A recent statement from a North Korean foreign ministry spokesperson directly targeted the trilateral military cooperation system among the U.S., Japan, and South Korea. A key phrase was "the unstable security environment in the region caused by Japan's remilitarization and South Korea's arms buildup, which are being pursued in earnest within the framework of the U.S.-Japan-ROK trilateral military cooperation system" [14]. In the same statement, North Korea reaffirmed that its status as a nuclear-weapon state, "made permanent by the country's highest law," would not be shaken by U.S. demands for denuclearization [14].

ROK-U.S.-Japan military exercises are proceeding as planned. The three countries continue to conduct joint drills targeting North Korea [7]. At the same time, conciliatory signals are being observed from Washington, with President Trump highlighting his "very good relationship" with Kim Jong Un and using the card of scaling back ROK-U.S. exercises [12]. This aligns with the context of Pyongyang's dual-track strategy of managing its channels with the U.S. and South Korea separately [3][6].

China's involvement is another characteristic of the current phase. Chinese Ministry of National Defense spokesperson Zhang Xiaogang identified Japan's plan to equip underwater drones with long-range missiles and its hypersonic weapon tests in Australia as "blatant military expansion." He criticized these moves as bearing a "striking resemblance" to Japan's pre-World War II militarism [4]. As North Korea effectively shares this framework for criticizing Japan, there is a growing assessment that the North Korean nuclear issue is changing its character to become a subordinate variable in the U.S.-China rivalry [3].

SIPRI's 2026 yearbook confirms this trend in a global context. It notes a clear trend of countries re-emphasizing nuclear weapons as an instrument of national power. The report diagnoses that amid growing risks of miscalculation and escalation, nuclear arms reduction efforts are regressing for the first time in decades [2][5][11].

3. Key Actors and Positions

North Koreaoperates two distinct communication channels. Commentaries under the anonymous byline of the "Military Commentary Board" leave room for a moderated tone regarding the new U.S. nuclear strategy. In contrast, official statements from the foreign ministry spokesperson reaffirm a hardline, principled stance on ROK-U.S. exercises and South Korea's military buildup [3][6]. This can be read as a calculation to maintain a pretext for deterring South Korea without damaging channels of contact with the United States.

South Koreais in a position where it must simultaneously advance the security logic for its Jangbogo-N nuclear-powered submarine project and explain its commitment to non-proliferation obligations. North Korea has preemptively framed the project itself as a catalyst for a regional nuclear domino effect [3]. President Trump's social media remarks concerning South Korea are cited as an example of the uncertainty within Washington regarding ROK-U.S. defense cost-sharing and the scale of joint exercises [13].

Japanis on a course to make increased defense spending a fait accompli under the Takaichi administration. About 160 items in the 8.9 trillion yen budget request were formulated as "item-based requests," for which specific amounts have not yet been determined. This leaves open the possibility that the final budget could be even larger than the initial request [10]. Some within the Japanese government interpret this request as an effort to reach a level "that the United States will find acceptable" [18].

United Statesis sending conflicting signals, simultaneously suggesting the restoration of channels with North Korea and the strengthening of ROK-U.S. military cooperation. President Trump's conciliatory approach is proceeding in parallel with the continuation of trilateral joint exercises [7][12]. This suggests that Washington's North Korea policy has not been consolidated into a single, coherent line.

Chinais intervening by framing Japan's defense budget increase and weapons system modernization as neo-militarism [4]. The way North Korea is aligning with this frame is a factor in recasting the North Korean nuclear issue as a subordinate variable in the U.S.-China rivalry [3].

4. Core Issues

The first issue is whether North Korea's dual-track strategy is sustainable. The key question is how long the gap between its conciliatory gestures toward the U.S. channel and its hardline stance toward South Korea can be managed [3][6].

The second issue is how to internationally explain South Korea's nuclear-powered submarine project. Whether this creates friction with the ROK-U.S. civil nuclear agreement and the international non-proliferation regime depends on how Seoul explains its security rationale in parallel with its non-proliferation obligations [3][6].

The third issue is the political finalization of Japan's defense budget increase. The actual scale of the military expansion will be determined by whether the 160 items left as item-based requests are funded and by the contents of the new Medium Term Defense Program to be announced this year [10][16].

The fourth issue is the extent to which the U.S.-China rivalry will absorb the North Korean nuclear problem. If China's criticism of Japan and North Korea's alignment with it continue, the space for managing the Korean Peninsula issue independently could shrink [3][4].

II. In-depth Analysis

In-depth Analysis: The Structural Origins of North Korea's Enhanced Tactical Nuclear Doctrine and the Regional Arms Race

1. Analysis of Root Causes

The root cause of the current situation is not a single event. It is the result of three axes—North Korea's doctrinal shift, South Korea's capability acquisition, and Japan's policy change—moving on different timelines and coincidentally converging in August.

The root cause on North Korea's side dates back to the 8th Party Congress in 2021. The doctrine of preemptive use of tactical nuclear weapons established at this congress was a structural decision to offset its conventional military inferiority to South Korea with nuclear weapons [9]. In early 2025, Kim Jong Un reaffirmed the continuity of this policy, mentioning a "new plan to accelerate the strengthening of all deterrence capabilities, including nuclear capabilities" [9]. In other words, the August statements are not a new policy but a re-articulation of an existing one. The North Korean foreign ministry's declaration that the U.S.'s "repeated expressions of its 'denuclearization' position" cannot shake its status as a nuclear-weapon state, which has been "made permanent by the country's highest law," is an extension of this [14].

The root cause on South Korea's side is the accumulated doubt about the credibility of extended deterrence. The Jangbogo-N nuclear-powered submarine project is read not merely as a force enhancement but as a political signal of a search for a supplement or alternative to the U.S. nuclear umbrella. North Korea's designation of this project as a "new risk factor for security in the Asia-Pacific region" and its mention of a potential "nuclear domino effect" [3] is, paradoxically, an admission by North Korea itself of the project's proliferation implications.

The root cause on Japan's side is twofold. One is the directness of the North Korean nuclear and missile threat, and the other is China's maritime expansion. A CFR analysis specifies that Japan's defense spending increase is a response to "North Korea's nuclear and missile capabilities and China's expanding maritime influence" [13]. This trend has gained political momentum since Prime Minister Takaichi took office. The 8.8908 trillion yen budget request for 2027 is not only an 80 billion yen increase from the previous year but is also seen by some as merely an "opening bid" for the new Medium Term Defense Program to be announced this year [10][18].

2. Structural Context

Security Structure: A Triple Deterrence Dilemma

The security structure in Northeast Asia involves three intertwined deterrence relationships: U.S. extended deterrence against North Korea, South Korea's demand to enhance its own deterrence capabilities, and Japan's dual deterrence against China and North Korea. These three relationships do not operate independently. The North Korean foreign ministry statement's criticism of "Japan's remilitarization and South Korea's arms buildup, which are being pursued in earnest within the framework of the U.S.-Japan-ROK trilateral military cooperation system" in a single sentence [14] shows that Pyongyang perceives this triple structure as a single threat axis.

The position of the United States in this structure is unique. The Trump administration is simultaneously sending conciliatory signals by highlighting its "very good relationship" with Kim Jong Un and suggesting a reduction in ROK-U.S. exercises [12], while also making contradictory moves to raise the level of deterrence against North Korea through discussions of a new nuclear strategy. This inconsistency opens up space for North Korea to pursue a dual-track strategy, responding to its U.S. and South Korean channels separately [3][6].

Political Structure: The Convergence of Domestic Politics and Hawkish Foreign Policy

In Japan, Prime Minister Takaichi's defense buildup is gaining domestic political momentum. The Ministry of Defense's decision to leave about 160 items in its budget request as unspecified "item-based requests" [10] is interpreted as an attempt to secure political flexibility during budget negotiations. The Hankyoreh reported this as an attempt to meet a level "that the United States will find acceptable" [18]. In other words, Japan's defense spending increase is not just a response to threats but also a political response to pressure within the U.S.-Japan alliance for greater burden-sharing.

In the North Korean system, the narrative of external threats is directly linked to internal cohesion. The Rodong Sinmun's characterization of Japan's budget proposal as a "military budget proposal aimed at further enhancing the war-fighting capabilities of the Self-Defense Forces" and its accusation that it "proves that its ambition for military great-power status is reaching a reckless stage" [1] is a typical example of how emphasizing external threats functions as a logic for domestic mobilization.

Economic Structure: The Fiscal Limits of Defense Spending Increases

Japan's defense spending increase has a fiscal ceiling. The current stage, where discussions are centered on whether spending will surpass 10 trillion yen (approximately 86 trillion won) from its current level of $62.2 billion, or 1.4% of GDP [13], reveals the tension between fiscal soundness and security demands [18]. This is also indirectly linked to the U.S. defense burden debate (related issue ranked 25th), as U.S. pressure on allies to increase their defense burden-sharing is already reflected in Japan's budget logic.

3. Historical Precedents and Comparative Cases

Comparison with the 2016–2017 THAAD Deployment Episode

During South Korea's 2016 decision to deploy the THAAD system, a similar triangular dynamic formed, involving North Korea's advancing nuclear and missile capabilities, South Korea's introduction of a defense system, and China's backlash. However, the current situation differs from that period. While THAAD was a defensive weapons system, the Jangbogo-N is a strategic asset with offensive potential, making North Korea's reaction and its "nuclear domino" framing [3] more visceral. Furthermore, this time China has established a separate axis of criticism aimed directly at Japan [4], expanding the 2016 bilateral ROK-China conflict into a multilateral structure of tension with more actors.

Continuity with the 2022–2023 Revision of Japan's Three Security Documents

Japan's current defense budget increase is an extension of the 2022 revision of its Three Security Documents, which included the decision to acquire counterstrike capabilities. At that time, China also framed Japan's policy shift as a revival of militarism. Spokesperson Zhang Xiaogang's recent criticism that Japan's plan to equip underwater drones with long-range missiles and its hypersonic weapon tests in Australia bear a "striking resemblance to Japan's pre-World War II militarism" [4] is a repetition of the same rhetoric. What is new this time, however, is that North Korea has effectively aligned with this anti-Japan criticism, creating a parallel front where both North Korea and China criticize the same target through separate channels.

Structural Similarity to Cold War Proliferation Chains

The trend of "re-emphasizing nuclear weapons as an instrument of national power," as pointed out in the SIPRI 2026 yearbook [2][5][11], is structurally similar to the multilateral nuclear proliferation concerns of the 1960s. At that time, there were also fears that one country's strengthening of nuclear capabilities would trigger a chain reaction, prompting neighboring countries to pursue their own response capabilities. In Northeast Asia today, North Korea's doctrinal enhancement, South Korea's discussion of nuclear propulsion for submarines, and Japan's buildup of advanced conventional weapons are nominally measures in different categories, yet they operate through the same mechanism of amplifying mutual threat perceptions.

4. Key Variables Shaping Future Developments

The variables that will shape the future situation can be narrowed down to three.

First is whether the new U.S. nuclear strategy will be formalized. It is currently at the internal Department of Defense discussion stage [3], but if it is converted into an official document, the level of North Korea's response is likely to escalate from anonymous commentaries to official foreign ministry statements [6]. This is directly linked to "changes in nuclear doctrine," a key monitoring point in the Korean Peninsula and North Korea issue area.

Second are the specific contents of Japan's Medium Term Defense Program. The scale and speed at which actual budgets are allocated to the 160-plus item-based requests in the plan, which Prime Minister Takaichi will announce this year [16], will determine the intensity of criticism from China and North Korea. Whether the budget surpasses 10 trillion yen [18] could act as a symbolic threshold.

Third is the consistency between U.S.-ROK military exercises and the Trump administration’s conciliatory signals toward North Korea. If these contradictory signals—scaling back exercises while strengthening a new nuclear strategy—continue to coexist [12], North Korea will retain an incentive to maintain its dual strategy toward the United States and South Korea. Conversely, if one of these signals becomes clearly dominant, North Korea’s response may also shed its dual nature and converge on a single approach. This dynamic should be monitored in conjunction with discussions on the effectiveness of the Nuclear Consultative Group (NCG) within the broader context of alliance and multilateral security issues.