North Korea's Series of Ballistic Missile Launches and the Rising Nuclear Debate between Japan and South Korea: A Serious Transformation of the Northeast Asian Security Environment

On April 8, 2026, North Korea launched multiple short-range ballistic missiles toward the Sea of Japan from the vicinity of Wonsan in eastern North Korea. According to the South Korean Joint Chiefs of Staff, the missiles launched around 8:50 AM flew approximately 240 kilometers. Additionally, one missile was launched around 2:20 PM the same day, estimated to have a range of over 700 kilometers and a maximum altitude of about 60 kilometers. All missiles fell into waters outside Japan's Exclusive Economic Zone (EEZ), and while there were no reports of damage to aircraft or vessels, the afternoon missile may have exhibited an irregular flight trajectory, indicating a military intent to complicate interception.

This series of launches follows projectiles (presumed to be large-caliber rockets or ballistic missiles, with South Korean media reporting the possibility of a launch failure) fired from around Pyongyang on April 7, marking two consecutive days of provocative actions. North Korea publicly displayed a new intercontinental ballistic missile (ICBM) during the 80th anniversary parade of the Workers' Party in October 2025, leaving no doubt about its ongoing advancements in ballistic missile technology. The Japanese government has strongly protested to North Korea through its embassy in Beijing, and Chief Cabinet Secretary Hirokazu Matsuno stated at a press conference that "we will make every effort to collect and analyze information."

The recent launches must be understood within a broader geopolitical context. With the prolonged Iran-Israel conflict in the Middle East, U.S. strategic interests and military resources are increasingly focused on that region. This "diversion of American attention" provides North Korea with an opportune moment for provocation. In a meeting on April 8 between Japan's Defense Minister Yasukazu Hamada and Australia's Defense Minister, there was a consensus that "as the world focuses on tensions in the Middle East, security challenges in the Indo-Pacific region are becoming apparent." On the same day, Defense Minister Hamada held a video conference with South Korean Defense Minister Lee Jong-sup to discuss North Korea's missile launches and the situation in Iran, reaffirming the continuation of trilateral security cooperation among Japan, South Korea, and the United States.

However, despite the strengthening of cooperation among allies, trust in U.S. extended deterrence (nuclear umbrella) in Northeast Asia is rapidly eroding. A recent report from the Council on Foreign Relations (CFR) cited by UPI on April 12 pointed out that South Korea and Japan have entered a deepening phase of "nuclear latency"—the state of having the technical capability to develop nuclear weapons while exercising restraint in weaponization. Professor John Mearsheimer of the University of Chicago argues that if U.S. strategic interests continue to drift away from Asia, the acquisition of independent nuclear capabilities by both countries could become a logical outcome.

Japan's nuclear infrastructure is among the best in the world. With approximately 45 tons of plutonium, it is said that nuclear weapons could be produced within months if a technical decision is made. Meanwhile, public opinion in South Korea is shifting significantly, with a survey by the Asan Institute for Policy Studies indicating that about 76% of respondents support domestic nuclear armament. President Trump's emphasis on "burden-sharing" has spread the perception among allies that U.S. protection is conditional, acting as a catalyst for nuclear discussions.

Energy security is also a significant driving force behind nuclear discussions. As disruptions to supply routes in the Middle East, including the Strait of Hormuz, become apparent, the strategic value of nuclear power is being re-evaluated for both Japan and South Korea, which rely on imports of oil and liquefied natural gas. South Korea is already permitted to enrich uranium for civilian use up to 20% under the revised U.S.-South Korea nuclear agreement, but further flexibility is needed for the realization of future nuclear submarines and small modular reactors (SMRs).

From North Korea's perspective, the consecutive missile launches carry a clear political message. As South Korean President Lee Jae-myung seeks dialogue with the North, North Korea treats South Korea as a "hostile state," demonstrating its lack of willingness for dialogue through military actions. The visit of Chinese Foreign Minister Wang Yi to North Korea on April 9, just before the missile launches, is noteworthy in the context of strengthening China-North Korea relations. China has warned of potential economic retaliation and military countermeasures against discussions of nuclear armament in Japan and South Korea, while North Korea has accused South Korea of "quasi-nuclear state" behavior.

The possibility of a "nuclear domino" effect in Northeast Asia is being discussed more realistically than ever. While the likelihood of Japan and South Korea immediately pursuing nuclear armament is considered low due to the risks of international sanctions and diplomatic isolation, the path of "strategic ambiguity" aimed at enhancing deterrence through the strengthening of nuclear-related capabilities is likely to become more pronounced. As of mid-April, U.S. forces are preoccupied with deployments in the Middle East, and concerns about the density of U.S. military forces in South Korea have been raised by former military officials within the country.

The recent series of missile launches by North Korea is not merely a one-off military provocation. It symbolizes a structural transformation in the Northeast Asian security environment characterized by the declining reliability of U.S. extended deterrence, the deepening of nuclear latency in Japan and South Korea, the diversion of strategic attention due to conflicts in the Middle East, and the strengthening of ties between China and North Korea. Japan needs to expedite the increase of its defense budget, the development of stand-off defense capabilities, and the enhancement of the effectiveness of the Japan-U.S. alliance, along with further deepening bilateral and multilateral security cooperation with South Korea and Australia. At the same time, a very difficult strategic balance is required between maintaining the nuclear non-proliferation regime and ensuring the reliability of deterrence.