Simultaneous US-China Military Exercises in the South China Sea

📡 THE SIGNAL — What Happened

Why it matters: In early 2026, the simultaneous deployment of large-scale military exercises by the US and China in the South China Sea has elevated the risk of accidental clashes to post-Cold War highs. This is not merely a military demonstration but a manifestation of structural escalation during a period of hegemonic transition, potentially undermining the security order across the entire Indo-Pacific.

• Military — From January to March 2026, the US Navy conducted "Valiant Shield 2026," a large-scale exercise in the South China Sea centered around two carrier strike groups. Participating forces are estimated to include over 25 vessels and more than 150 aircraft.
• Military — The Chinese People's Liberation Army Navy (PLAN) conducted the "South China Sea Sharp Sword 2026" (南海利剣2026) exercise across the entire South China Sea during the same period. Over 30 vessels, including the aircraft carrier "Fujian," participated, deploying large-scale training including simulated amphibious landing operations.
• Geopolitics — The exercise areas overlapped around the Spratly Islands (南沙諸島) and Paracel Islands (西沙諸島), leading to multiple instances where vessels and aircraft from both militaries approached within tens of kilometers.
• Diplomacy — ASEAN nations issued a joint statement expressing "serious concern," but differences in sentiment among member states prevented concrete calls for action. While the Philippines and Vietnam showed the strongest apprehension, Cambodia and Laos maintained a neutral stance.
• Economy — The South China Sea is a maritime trade route through which approximately one-third of global trade (worth about $5.3 trillion annually) passes. Rising military tensions directly lead to increased maritime insurance premiums and risks of supply chain disruptions.
• International Law — China continues to disregard the 2016 Permanent Court of Arbitration ruling (which rejected China's "nine-dash line" claims). The US increased the frequency of its "Freedom of Navigation Operations (FONOP)" from twice a month in 2025 to 3-4 times a month in 2026.
• Technology — China deployed mobile launchers for anti-ship ballistic missiles (DF-21D/DF-26) on its artificial islands in the South China Sea. In response, the US accelerated the operational deployment of its MQ-25 Stingray unmanned aerial refueler.
• Alliances — The Quadrilateral Security Dialogue (QUAD) — Japan, the US, Australia, and India — discussed the South China Sea situation at their foreign ministers' meeting in February 2026. For the first time, the Japan Maritime Self-Defense Force dispatched two destroyers to a US military exercise in the South China Sea, effectively conducting a joint exercise.
• Domestic Politics — 2026 is a US midterm election year, making a tough stance on China a domestic political imperative for the Biden administration (or its successor). On the Chinese side, with the Party Congress in 2027 approaching, the Xi Jinping leadership finds compromise on territorial issues difficult.
• Military Communications — Although the US-China military hotline (crisis management communication channel) was reopened in 2023, trust-building at the operational level has not progressed, leaving doubts about the immediate response capability in the event of accidental contact.
• Resources — The South China Sea is estimated to hold 11 billion barrels of oil and 190 trillion cubic feet of natural gas, making concessions difficult for both countries from an energy security perspective.

To understand the escalating US-China confrontation in the South China Sea, it is necessary to take a long-term view of structural changes spanning at least half a century.

During the Cold War, the South China Sea remained relatively stable under the overwhelming naval power of the United States. China's southward expansion progressed incrementally, such as its seizure of the Paracel Islands from Vietnam (then South Vietnam) in 1974 and its clash with the Vietnamese Navy at Johnson South Reef in the Spratly Islands in 1988, leading to its occupation. However, within the broader framework of US-Soviet rivalry, these were treated as "peripheral events."

A turning point was the 1995 Mischief Reef incident. China constructed structures on Mischief Reef, located within the Philippines' Exclusive Economic Zone (EEZ), effectively beginning its militarization. This incident clearly demonstrated China's intent to accelerate its maritime expansion under the post-Cold War "unipolar system." However, the US was focused on other regional issues such as Iraq, Bosnia, and Somalia, and its interest in the South China Sea was limited.

In the 2000s, China's economic rise and military modernization accelerated. In 2009, China submitted a "nine-dash line" map to the UN, claiming historical rights over almost the entire South China Sea, which shocked the international community. In response, then-Secretary of State Hillary Clinton of the Obama administration declared at the 2010 ASEAN Regional Forum that "freedom of navigation in the South China Sea is a US national interest," clearly signaling the US's serious commitment to the security of this region. This was the core of the so-called "Pivot to Asia" policy.

Since 2013, China has rapidly advanced "island building," reclaiming large areas of reefs and shoals in the Spratly Islands to construct artificial islands. 3,000-meter-class runways were built on Fiery Cross Reef, Subi Reef, and Mischief Reef, along with radar facilities, anti-air and anti-ship missiles, and hangars. Despite President Xi Jinping's promise to President Obama at their 2015 summit that China would "not militarize the South China Sea," this militarization steadily progressed.

The 2016 Permanent Court of Arbitration ruling was a landmark decision that completely rejected China's claims of historical rights based on the nine-dash line. However, China dismissed it as "a piece of paper" and refused to acknowledge the legal binding force of the ruling. At this point, the path to dispute resolution through international law was effectively closed.

The Trump administration (first term) strengthened "Freedom of Navigation Operations" and increased the US military presence in the South China Sea. The Biden administration further expanded this, adopting a multilateral approach that emphasized cooperation with allies. It advanced the construction of a security network surrounding China, including the establishment of AUKUS (Australia-UK-US security partnership), the elevation of QUAD to a leaders' level, and the expansion of the Enhanced Defense Cooperation Agreement (EDCA) with the Philippines.

However, from China's perspective, these "deterrence enhancements" were nothing less than "containment." In response, China accelerated its military buildup and coercive actions, deepening the "security dilemma." Since 2023, incidents of water cannon attacks and collisions by the China Coast Guard against Philippine resupply vessels have become frequent, and tensions around Second Thomas Shoal (仁愛礁) have reached dangerous levels.

The situation in 2026 is at a "critical juncture" of this decades-long structural conflict. The US needs to demonstrate the reliability of its alliance network to maintain its hegemony, while China, under the national goal of "the great rejuvenation of the Chinese nation," finds territorial concessions politically impossible. In a structure where neither side can back down, the risk of accidental contact leading to unintended escalation is higher than ever before. This "spiral of conflict" forms a self-reinforcing feedback loop where one party's deterrent actions heighten the other's perception of threat, prompting further military buildup, and has entered a phase where deceleration is difficult without external intervention.

The delta: The simultaneous US-China military exercises in early 2026 indicate a structural shift from previous "action-reaction" sequential escalation to a state of "constant confrontation." The situation where both sides conduct large-scale exercises simultaneously in the same waters not only dramatically increases the probability of accidental clashes but also signifies the arrival of a new phase where "escalation without prior notice" becomes the norm.