The Impact of the Middle East War on Northeast Asia: The Shift of U.S. Military Forces and Changes in Regional Security

In mid-March 2026, the U.S. military decided to deploy the amphibious assault ship USS Tripoli, homeported in Sasebo, Nagasaki Prefecture, along with over 2,000 Marines to the Middle East. This decision came in response to President Donald Trump's announcement of an escalation in military action as the war with Iran entered its third week. According to the Wall Street Journal and Fox News, the 31st Marine Expeditionary Unit, based in Okinawa, is set to deploy to the region, with the USS Tripoli expected to arrive within 1 to 2 weeks.

This troop movement is a response to the intensification of Iranian attacks in the Strait of Hormuz, through which approximately 20% of the world's crude oil transportation passes. However, the large-scale redeployment of U.S. military assets from the Indo-Pacific region to the Middle East raises serious security concerns for allies in Northeast Asia. Earlier this week, the Washington Post and South Korean media reported that the U.S. military plans to transfer part of its missile defense systems aimed at defending against North Korea from South Korea to the Middle East. This is said to include the Terminal High Altitude Area Defense (THAAD) and Patriot systems.

While the U.S. force realignment does not fundamentally change the existing threat perception in Northeast Asia, it could lead to a short-term decrease in deterrence. In particular, Japan and South Korea face a dual challenge from China's military rise and North Korea's enhanced nuclear and missile capabilities, and even a temporary reduction in U.S. military presence could have subtle effects on the regional security balance. The South Korean Defense Intelligence Agency reported on March 1 that North Korea has transported a total of 33,000 weapon containers to Russia's Kursk region since 2024. This movement indicates that North Korea is deepening its military cooperation with Russia, further heightening tensions on the Korean Peninsula.

China's military activities cannot be ignored either. According to the U.S. Department of Defense's "Military Power of China 2025" report, the People's Liberation Army (PLA) has acquired the capability to threaten U.S. military bases in the western Pacific through the expansion of long-range precision strike weapons. Their range reaches 2,800 to 3,700 kilometers from the Chinese mainland, putting key bases such as Okinawa and Guam within striking distance. A report from the Stimson Center in December 2024 pointed out that China's ballistic and cruise missiles have the capability to destroy runways at Naha Air Base, Kadena Air Base, and Marine Corps Air Station Futenma, making aircraft takeoffs and landings impossible. The report estimates that such attacks could render U.S. military bases non-operational for approximately 280 hours (about 11-12 days) for fighter operations and about 800 hours (over 33 days) for aerial refueling operations.

Against this backdrop of threat perception, Japan is enhancing the military functions of Iwo Jima. The Ministry of Defense plans to consider improvements to the air and port infrastructure on Iwo Jima in the next fiscal year, including runway extensions, strengthening port facilities, and installing floating docks to accommodate large vessels. Furthermore, to enable rapid responses to foreign aircraft and vessels, the permanent deployment of Self-Defense Force fighter jets is also being considered. This move aims to complement the strengthening of defense capabilities in Okinawa and Kyushu and to fill the "monitoring gap" on the Pacific side of the Japanese archipelago.

Iwo Jima is strategically important, located about 1,200 kilometers south of Tokyo, for managing a vast exclusive economic zone. It also contributes to securing seabed resources, including rare earth minerals discovered in nearby Pacific islands. Additionally, in light of increased activities suspected to involve carrier operations beyond China's first island chain and seabed surveys aimed at monitoring undersea cables, the role of Iwo Jima is becoming increasingly significant. According to a Naval News article from December 2025, Iwo Jima has the only runway in the Pacific capable of operating Self-Defense Force fighter jets, serving as an alternative base if the air bases in Okinawa or Yonaguni Island become incapacitated due to attacks.

The U.S. "Agile Combat Employment (ACE)" concept aims to complicate enemy targeting by dispersing aircraft and support units across numerous temporary and makeshift bases, enabling rapid movement and flexible operations while maintaining combat capability under attack. The enhancement of military functions on Iwo Jima suggests that Japan is seeking to elevate its role as a strategic hub along the second island chain. The second island chain connects the Ogasawara Islands, the Volcano Islands, the Mariana Islands, and Western New Guinea.

However, several challenges have been pointed out regarding the effectiveness of the ACE concept. In an article in Proceedings magazine in July 2024, Michael Blaser noted that ACE is based on unrealistic assumptions about enemy capabilities and underestimates advancements in surveillance and attack technologies. First, ACE assumes that the enemy does not possess long-range missiles capable of simultaneously attacking multiple dispersed air bases, but China's extensive missile forces can strike numerous bases at once. Second, ACE presumes that the enemy's targeting cycle is slower than the U.S. military's sortie generation, but advancements in artificial intelligence, satellite surveillance, and automated image analysis have enabled the enemy's kill chain to shrink within 24 hours, allowing for rapid targeting of dispersed aircraft. Blaser warns that without deception and camouflage measures, ACE risks becoming ineffective against modern reconnaissance and attack systems.

On the other hand, Guam, a key part of the second island chain, faces similar vulnerabilities. A report from the U.S. Government Accountability Office (GAO) in May 2025 pointed out that Guam remains vulnerable despite U.S. missile defenses. Currently, Guam is defended by a single THAAD battery consisting of six missile launchers and one radar, with occasional additional protection provided by U.S. Navy vessels. The report states that while the Department of Defense plans to build a more robust integrated system known as the "Guam Defense System," the capability to counter advanced ballistic, cruise, and hypersonic missiles is expected to be fully deployed by the late 2020s to early 2030s.

Given this situation, the impact of the U.S. war in the Middle East on Northeast Asia goes beyond mere temporary force transfers. It raises fundamental questions about the regional military balance, alliance structures, and long-term security policies. Japan's strengthening of Iwo Jima and the expansion of military cooperation between the U.S. and Japan (including joint missile production and enhanced sharing of classified information) are part of the response to this fluid environment, but considering the unresolved limitations of China's expanding missile range and dispersed base deployment concepts, their effectiveness remains uncertain. The security environment in Northeast Asia is entering a new era of instability due to changes in U.S. strategic priorities and advancements in military technology within the region.