US-China Military Standoff in the

📡 THE SIGNAL — What Happened

Why it matters: In early 2026, US and Chinese military exercises in the South China Sea overlapped in time and space, raising the risk of accidental conflict to its highest level since the end of the Cold War. This tension fundamentally shakes Japan's security policy and accelerates the reorganization of order across the Indo-Pacific.

• Military Trends — From January to March 2026, the US Navy conducted "freedom of navigation" operations in the South China Sea at an unprecedented pace of more than three times a month, simultaneously deploying two carrier strike groups.
• Military Trends — The Chinese People's Liberation Army newly deployed HQ-9B long-range surface-to-air missile systems on three artificial islands in the Spratly Islands, significantly enhancing its A2/AD (Anti-Access/Area Denial) capabilities in the surrounding airspace.
• Diplomacy — Negotiations for the Code of Conduct (COC) in the South China Sea effectively collapsed at the ASEAN Defense Ministers' Meeting at the end of 2025, rendering multilateral conflict deterrence frameworks dysfunctional.
• Alliance Relations — The Japanese and US governments agreed to regularize joint patrols in the South China Sea at their "2+2" meeting in February 2026, leading to an increased frequency of Japan Maritime Self-Defense Force destroyers sailing alongside US vessels.
• Economy — The value of global trade passing through the South China Sea amounts to approximately $5.3 trillion annually, with about one-third of the world's maritime trade relying on this area.
• Domestic Politics — In Japan, opposition parties oppose an expansive interpretation of security-related legislation, while within the ruling party, a policy conflict has surfaced regarding the prioritized deployment of "counterstrike capabilities" to the southwestern region.
• Technology — China's DF-27 anti-ship ballistic missile, reportedly deployed in late 2025, is said to have a range of 4,000 km and is analyzed to possess the capability to target US military bases in Guam.
• Resources — The South China Sea is estimated to hold 11 billion barrels of oil and 190 trillion cubic feet of natural gas, with China, Vietnam, and the Philippines in conflict over resource development rights.
• Legal Framework — China continues to disregard the 2016 South China Sea arbitration ruling by the Permanent Court of Arbitration (which invalidated the nine-dash line), leaving the path to international legal resolution blocked.
• Military Incidents — In February 2026, an incident occurred near Scarborough Shoal where a US Navy P-8A patrol aircraft and a Chinese Navy J-16 fighter jet came within approximately 5 meters of each other, prompting the US Department of Defense to protest it as "an extremely dangerous act."
• Cyber — From late 2025 to early 2026, cyberattacks targeting communication systems at US military bases in Japan surged, with the involvement of a suspected Chinese-linked APT group.
• Public Opinion — A Japanese public opinion poll in March 2026 showed that the percentage of respondents who considered "China a security threat" reached a record high of 82%, and support for increased defense spending rose to 67%.

To understand the current escalation of US-China tensions in the South China Sea, it is necessary to read it through at least three historical contexts.

First, there is the relationship between China's "century of humiliation" narrative and its maritime expansion. For approximately 100 years, from the late Qing Dynasty to the founding of the People's Republic of China, China experienced its coastal areas being ravaged by great powers. Since the Opium Wars (1840), China has consistently been in a passive position regarding threats from the sea. When Deng Xiaoping initiated reform and opening up in the late 1970s, naval modernization was initially deferred, but its strategic intent—namely, the gradual expansion from near-sea defense to far-sea defense—was clearly documented as Admiral Liu Huaqing's "Island Chain Strategy." The concept of the First Island Chain (Kyushu-Okinawa-Taiwan-Philippines) as "China's inland sea" rapidly materialized under the Xi Jinping administration in the form of artificial island construction and militarization. Since 2013, China has reclaimed land on Subi Reef, Mischief Reef, Fiery Cross Reef, and others, constructing runways, radar facilities, and missile launch pads, irreversibly altering the military presence in the South China Sea.

Second, there is the evolution of US Indo-Pacific strategy. For the US during the Cold War, the South China Sea was merely a secondary theater for containing the Soviet Union. However, with the Obama administration's "Pivot to Asia" declaration in 2011, the US shifted its focus to re-strengthening its military presence in the Western Pacific. The first Trump administration explicitly positioned China as a "strategic competitor" and significantly increased the frequency of "freedom of navigation" operations in the South China Sea. The Biden administration established AUKUS (Australia-United Kingdom-United States security partnership) and promoted deterrence against China through strengthening alliance networks. The current administration, which took office in 2025, has further hardened the previous administration's stance, rapidly expanding military interoperability with allies under the banner of "integrated deterrence."

Third, and most importantly, there is the structural pressure of "Thucydides's Trap." Professor Graham Allison of Harvard University points out that in history, 12 out of 16 instances where strategic competition intensified between an existing hegemon (the US) and a rising power (China) led to war. The South China Sea is the frontline where this structural conflict physically manifests, a geographical nexus where the core interests of both nations directly collide.

So, why "now"? The sharp increase in tensions in early 2026 is due to the simultaneous convergence of multiple factors. First, China's domestic economic slowdown (GDP growth rate in 2025 remained at 4.2%, below the government target of 5%) is motivating the Xi Jinping administration to adopt a hardline stance externally. Historically, authoritarian regimes tend to deflect domestic economic discontent with external nationalism. Second, as part of the US political cycle, new administrations tend to send diplomatic signals of "strength" early in their tenure, and strengthening presence in the South China Sea is a typical means to do so. Third, as a technological factor, the maturation of China's A2/AD capabilities (especially the DF-21D and DF-27 anti-ship ballistic missiles) has relatively diminished the conventional deterrence of US carrier strike groups, creating a perception in China that "now is the time to challenge." Fourth, the division within ASEAN—with Cambodia and Laos taking pro-China stances, while the Philippines and Vietnam strengthen their pro-US positions—is neutralizing multilateral conflict management mechanisms.

For Japan, this situation means that the gray zone between "peace" and "emergency" is rapidly expanding. While the 2015 amendment to security legislation made it possible to exercise limited collective self-defense, the extent to which joint operations with US forces in the South China Sea fall within this framework remains legally ambiguous. The escalation of tensions in 2026 will be a litmus test for Japan's ability to maintain this ambiguity.

The delta: The US-China confrontation in the South China Sea has entered a qualitatively new phase of accidental conflict risk due to the collapse of COC negotiations at the end of 2025 and the frequent occurrence of abnormal military close-encounter incidents in early 2026. The decisive change is that tensions, which previously remained within the scope of diplomatic rhetoric and military shows of force, have shifted to a stage where incidents involving physical contact are becoming normalized, and the effectiveness of bilateral channels for escalation management (the US-China military hotline) has significantly deteriorated.