Structural Transformation of Security in Northeast Asia — Reconfiguration of Deterrence from the Korean Peninsula to the Taiwan Strait by Spring 2026

On May 17, 2026, in the early hours, North Korea launched multiple ballistic missiles toward the Sea of Japan from the vicinity of Sinpo in South Hamgyong Province. According to the South Korean Ministry of National Defense, the launch began around 6:10 AM local time, and the missiles reportedly flew approximately 140 kilometers. Japan's NHK also confirmed this, and the South Korean Joint Chiefs of Staff issued a statement saying, "We are closely monitoring North Korea's military activities under the strong joint defense posture of South Korea and the United States." The U.S. Indo-Pacific Command also stated, "At this time, there is no immediate threat to U.S. personnel, territory, or allies," while continuing consultations with regional allies.

Sinpo, the launch site for this event, is known as a strategic point where North Korea's submarine base is located. For this reason, South Korean military authorities are reportedly analyzing the possibility that the launch included submarine-launched ballistic missiles (SLBMs) in addition to conventional land-based launches, according to Yonhap News. It is also noteworthy that the launch occurred shortly after Rafael Grossi, Director General of the International Atomic Energy Agency (IAEA), visited South Korea and called for the resumption of denuclearization talks with North Korea. The South Korean Ministry of National Defense strongly condemned the launch as "a clear violation of United Nations Security Council resolutions and a provocative act that escalates tensions on the Korean Peninsula."

This launch is the latest in a series of military activities conducted by North Korea since the beginning of 2026. In April of this year, the National Defense Science Institute and the Missile Bureau conducted a large-scale weapons test over three days, which included electromagnetic weapon systems, dispersion tests of carbon fiber dummy bombs, mobile short-range air defense missile systems, and the launch of ballistic missiles equipped with cluster bomb warheads. Kim Jong-un, General Secretary of the Workers' Party of Korea, recently inspected tactical guided weapon facilities and instructed the expansion of missile production capacity by 250 percent and the construction of additional factories, according to state media. This is seen as an indication of an intention to accumulate achievements in both defense policy and economic strategy ahead of the Workers' Party Congress scheduled to be held for the first time in five years.

The Japanese government's response was swift and resolute. Defense Minister Shinjiro Koizumi, despite being on a visit to Australia, stated, "North Korea's actions are absolutely unacceptable, and its ballistic missile and nuclear development programs pose a direct threat to regional and international stability," emphasizing the importance of close cooperation and full readiness between Japan, the U.S., and South Korea. This statement is set against the backdrop of Japan's ongoing largest defense force enhancement since World War II.

On December 26, 2025, the cabinet led by Prime Minister Sanae Takaichi decided on a record defense budget of 9.04 trillion yen (approximately $58 billion) for the fiscal year 2026. This represents a 3.8 percent increase from the previous year and marks the twelfth consecutive year of record highs. Notably, the specifics of the budget are significant. Just looking at the Japan Maritime Self-Defense Force, 51 billion yen is allocated for various test preparation costs for two Aegis-equipped ships (ASEV) with a standard displacement of 12,000 tons, 66.7 billion yen for the construction of the sixth ship of the new FFM (Mogami-class enhanced version, with a full displacement of approximately 6,200 tons) decided by Australia, 77.3 billion yen for the construction of the tenth Taigei-class submarine, and 64.06 billion yen for the establishment of a multi-layered coastal defense system named SHIELD.

The SHIELD concept stands for Synchronized, Hybrid, Integrated and Enhanced Littoral Defense, and is an integrated coastal defense architecture that combines surface ship-launched UAVs, small shipborne UAVs, and small multi-purpose USVs. The V-BAT from U.S. company Shield AI is being considered for installation on the new OPV (Sakura-class patrol vessel, with a standard displacement of 1,900 tons) and the new FFM. Additionally, 22.84 billion yen is budgeted for the mass production costs of an improved version of the Type 12 surface-to-ship guided missile launched from ships, and 10.24 billion yen for the mass production costs of a new long-range cruise missile that can be launched from submarine torpedo tubes, indicating that Japan's counterattack capabilities are becoming a reality in both name and substance.

Such fundamental changes in Japan's defense posture are not limited to domestic equipment procurement. In April and May 2026, Japan participated on a large scale for the first time in the U.S.-Philippines joint exercise "Balikatan 2026," deploying approximately 17,000 troops. The most notable aspect of this exercise was the live firing of Japan's Type 88 surface-to-ship guided missile at a target ship located 75 kilometers offshore from Ilocos Norte in northern Luzon. This is considered the first instance of Japan's offensive missile being fired abroad since World War II, and the Chinese Foreign Ministry strongly condemned it as "evidence of Japan's new militarism."

Furthermore, during the same exercise, the U.S. Army's Typhon system was live-fired for the first time after being deployed in the Philippines, successfully destroying a target approximately 630 kilometers away with a Tomahawk cruise missile. The Typhon is a medium-range strike system capable of launching SM-6 and Tomahawk missiles, and its deployment in the Philippines has been a point of intense backlash from China. Chris Gardner of the Canberra-based Institute for Regional Security analyzed, "The message of this exercise is clear—any use of force against the Philippines or changes to the status quo regarding Taiwan are not acceptable at this time."

Tensions surrounding the Taiwan Strait are also rising concurrently. On April 20, 2026, China's aircraft carrier Liaoning passed through the Taiwan Strait. According to Taiwan's Ministry of National Defense, this is the first passage of a Chinese aircraft carrier through the Taiwan Strait since the Fujian in December of last year. Three days prior, on April 17, the Japan Maritime Self-Defense Force's destroyer Ikazuchi passed through the Taiwan Strait. This date coincides with the anniversary of the Treaty of Shimonoseki, which ended the First Sino-Japanese War (signed on April 17, 1895), and the Chinese side reacted by calling it "a dangerous attempt that undermines peace and stability in the Taiwan Strait." Chinese Foreign Ministry spokesperson Guo Jiaqin condemned it as "a dangerous conspiracy by certain Japanese forces to militarily intervene in the Taiwan Strait."

These movements indicate that the security structure in Northeast Asia is qualitatively shifting from a stage of "crisis deterrence" to "permanent deterrence." North Korea's missile provocations have become a constant threat rather than sporadic crises, and the Taiwan Strait has become the frontline in the gray zone struggle over the freedom of international navigation and the maintenance of territorial status quo. In response to this structural change, Japan is simultaneously advancing a multi-layered approach that includes achieving a defense budget of 2 percent of GDP, developing stand-off missile capabilities, large-scale introduction of unmanned systems, enhancing interoperability with allies, and gradually relaxing arms export regulations.

In addition to the new FFM export contract to Australia (signed in April 2026, with Mitsubishi Heavy Industries constructing it at the Nagasaki shipyard), discussions on the transfer of defense equipment with the Philippines, expressions of interest from New Zealand, and interest in high-speed patrol boats from Indonesia—these are all evidence that Japan's defense industry is transitioning from being merely a supplier for the Self-Defense Forces to becoming an international supplier of defense equipment. According to a report by CNBC (dated May 14, 2026), Professor Stephen Nagy of International Christian University evaluated, "Japan's engineering technology is at the highest level, and the next-generation fighter jet GCAP being developed in collaboration with the UK and Italy will be the pinnacle of that," while also pointing out the challenges of a lack of international marketing experience and price competitiveness.

In the spring of 2026 in Northeast Asia—where Kim Jong-un's orders for missile factory expansions, the deployment of stand-off missiles by the Self-Defense Forces, aircraft carriers and escort ships traversing the Taiwan Strait, and the sounds of live-fire exercises echoing in the South China Sea are forming a significant geopolitical wave. Within this wave, the deterrence cooperation between Japan, the U.S., and South Korea, as well as the maritime security cooperation between Japan, the U.S., and the Philippines, has moved from the planning stage to implementation and operation. The remaining challenge is how to manage the security dilemma where the rapid strengthening of this deterrence paradoxically provokes escalation from the opposing side. The balance of power in Northeast Asia is being redefined at an unprecedented speed.