U.S.-China Military Tensions in the South China

📡 THE SIGNAL — What Happened

Why it matters: In early 2026, US and Chinese military exercises in the South China Sea are overlapping in time and space, raising the risk of accidental clashes to post-Cold War highs. A structure is forming where allies, including Japan, could be drawn into a chain reaction, marking a turning point for the security order across the Indo-Pacific.

• Military Trends — From January to March 2026, the US Navy conducted "Freedom of Navigation Operations" (FONOPs) in the South China Sea at a record frequency of over three times a month. An unprecedented posture of simultaneously deploying two aircraft carrier strike groups was adopted.
• Military Trends — The Chinese People's Liberation Army (PLA) conducted large-scale live-fire exercises in the South China Sea in February 2026. The exercise area was set broadly from the Paracel Islands to the Spratly Islands, affecting civilian navigation.
• Diplomacy — The operation of the US-China military hotline, agreed upon at the APEC San Francisco summit in November 2025, has effectively stalled since the beginning of 2026. Reports indicate that the Chinese side has delayed responding to communication tests.
• Alliance Relations — Japan achieved over 2% of GDP for its defense budget for the first time in fiscal year 2026. Plans to deploy long-range missiles to the Nansei Islands are being accelerated, and troop reinforcements on Yonaguni Island and Ishigaki Island are being expedited.
• Economy — Trade volume passing through the South China Sea amounts to approximately $5.3 trillion annually, with about 30% of global trade transiting this area. The heightened risk of conflict directly impacts global supply chains through increased insurance premiums.
• Legal Framework — China continues to ignore the 2016 arbitral tribunal ruling (which rejected China's nine-dash line claim). Artificial islands in the Spratly Islands are reportedly equipped with radar facilities, runways, and anti-ship missiles.
• Technology — China Coast Guard vessels, equipped with military-grade water cannons and acoustic weapons, have intensified their harassment of Philippine resupply vessels since late 2025. So-called "gray zone tactics" have become normalized.
• Domestic Politics — In the US, with the 2026 midterm elections approaching, a hardline stance against China has become a bipartisan political asset. Neither party can politically tolerate a retreat in the South China Sea.
• Domestic Politics — In China, the Xi Jinping administration has positioned the construction of a "maritime power" as a core interest, linked to rising domestic nationalism. Concessions in the South China Sea risk directly threatening its power base.
• Alliance Relations — The Philippines has expanded the rotational deployment of US forces based on the 2023 Enhanced Defense Cooperation Agreement (EDCA) between the US and the Philippines. The China-Philippines dispute over Ayungin Shoal (Second Thomas Shoal) has become the frontline of US-China rivalry.
• Regional Affairs — ASEAN countries are increasingly frustrated by the stagnation of negotiations for a Code of Conduct (COC) in the South China Sea, but China's economic influence continues to prevent a unified response.
• Military Technology — The US military has deployed the Typhoon intermediate-range missile system to northern the Philippines. China has strongly reacted to this as "destroying strategic stability" and has hinted at countermeasures.

To understand the current escalation of US-China tensions in the South China Sea, at least three historical contexts must be overlaid.

First, there is China's long-term trajectory of maritime expansion. The "eleven-dash line" drawn by the Republic of China in 1947 (later revised to the "nine-dash line" by the People's Republic of China) has been the basis for its territorial claims over almost the entire South China Sea. However, it was only after the 2010s that this claim began to be backed by military presence. Large-scale artificial island construction in the Spratly Islands, which began around 2013, proceeded at a speed exceeding international expectations, and militarization accelerated even after the 2016 arbitral tribunal ruling legally rejected China's claims. The Xi Jinping administration has positioned the construction of a "maritime power" as an indispensable element of the great rejuvenation of the Chinese nation, making effective control of the South China Sea a pillar of its domestic legitimacy.

Second, there is the shift in the US Indo-Pacific strategy. The Obama administration's "pivot to Asia" was grand in concept but limited in execution due to ongoing involvement in the Middle East. The first Trump administration (2017-2021) championed a "free and open Indo-Pacific" but left alliance relationships unstable. The Biden administration (2021-2025) built a multi-layered network of deterrence against China through AUKUS, US-Japan-Philippines trilateral cooperation, and Quad strengthening. The second Trump administration (2025-) has inherited some of the previous administration's alliance networks but is pursuing a more unilateral China policy. As a result, the US military presence in the South China Sea has expanded quantitatively, but coordination mechanisms with allies are more prone to friction.

Third, there is the structural change in the regional order. Post-Cold War stability in Asia was supported by three pillars: overwhelming US military power, China's focus on economic growth, and multilateral dialogue mechanisms centered on ASEAN. However, all three pillars have weakened due to the narrowing military power gap between the US and China, the division of ASEAN by China's expanding economic influence, and the prolonged stagnation of negotiations for a Code of Conduct (COC) in the South China Sea. Especially since the 2020s, with the normalization of the China Coast Guard's "gray zone operations," the very definition of traditional military conflict has become ambiguous, making escalation management significantly more difficult.

So, why is the risk particularly high "now"? There are multiple direct triggers. First, physical clashes between China and the Philippines over the resupply of Ayungin Shoal intensified from late 2025, bringing the application of the US-Philippines Mutual Defense Treaty to the forefront of policy discussions. Second, the US deployment of the Typhoon intermediate-range missile system to northern the Philippines in 2025 led China to perceive its South China Sea strategy as being under direct military threat. Furthermore, the effective dysfunction of US-China military dialogue channels since early 2026 has structurally increased the risk of accidental contact escalating into uncontrollable situations.

In addition, the domestic politics of both countries are creating an "escalator from which they cannot get off." In the US, with the 2026 midterm elections approaching, being perceived as soft on China is tantamount to political suicide. In China, concessions on maritime interests are considered impossible for the Xi Jinping administration to maintain its power base in its third term. This extreme narrowing of political space for diplomatic solutions on both sides is the structural factor making the South China Sea situation in 2026 more dangerous than at any previous time.

Historically, military conflicts between great powers do not always begin with intentional declarations of war. Rather, they often start with "accidental" incidents triggered when both sides misinterpret each other's intentions, communication channels for de-escalation fail, and domestic politics do not allow for retreat. The current situation in the South China Sea is precisely meeting these conditions.

The delta: Since the beginning of 2026, the operational tempo of both US and Chinese militaries in the South China Sea has simultaneously accelerated, while military dialogue channels designed to prevent accidental clashes have effectively become dysfunctional. This means that tensions in the South China Sea are transitioning from "managed competition" to a phase of "uncontrollable escalation risk." The critical change is that the domestic politics of both sides have created a structure that does not allow for "retreat," severely narrowing diplomatic off-ramps.