Risk of Collision in South China Sea US-China Military Dr
In early 2026, large-scale military exercises by both US and Chinese forces simultaneously in the South China Sea have brought the risk of accidental collision to its highest level since the Cold War. This tension directly impacts Japan's sea lane defense and economic security, potentially shaking the order of the entire Indo-Pacific region to its core.
── Understand in 3 points ─────────
- • From January to March 2026, the US Navy conducted large-scale exercises in the South China Sea, centered around the USS Carl Vinson Carrier Strike Group. This included joint exercises with the Philippine and Australian navies.
- • The Chinese People's Liberation Army, primarily from its Southern Theater Command, simultaneously conducted military exercises, including live-fire drills, around the Paracel and Spratly Islands. A large number of China Coast Guard vessels were also mobilized.
- • Multiple incidents occurred where US and Chinese naval vessels approached within several hundred meters of each other, sharply increasing the risk of accidental collision.
── NOW PATTERN ─────────
The military confrontation between the US and China in the South China Sea exhibits a structural pattern where an "escalation spiral" self-reinforces, and the potential for "power overreach" and "alliance strain" in both countries interact.
── Probability and Response ──────
• Base case 55% — Regular use of US-China military-diplomatic channels. Resumption of substantive discussions on a Code of Conduct (COC) for the South China Sea at ASEAN-related meetings. Signaling by both leaders explicitly stating "avoidance of conflict."
• Bull case 15% — Agreement on concrete military confidence-building measures at a US-China summit. China's voluntary reduction in the scale of military exercises in the South China Sea. Decrease in the frequency of US freedom of navigation operations.
• Bear case 30% — US-China military hotline inoperable. China's unilateral establishment of restricted navigation zones in the South China Sea. Direct use of force against the Philippine military. Dispatch of additional US carrier strike groups.
📡 The Signal — What Happened
Why it matters: In early 2026, large-scale military exercises by both US and Chinese forces simultaneously in the South China Sea have brought the risk of accidental collision to its highest level since the Cold War. This tension directly impacts Japan's sea lane defense and economic security, potentially shaking the order of the entire Indo-Pacific region to its core.
- Military — From January to March 2026, the US Navy conducted large-scale exercises in the South China Sea, centered around the USS Carl Vinson Carrier Strike Group. This included joint exercises with the Philippine and Australian navies.
- Military — The Chinese People's Liberation Army, primarily from its Southern Theater Command, simultaneously conducted military exercises, including live-fire drills, around the Paracel and Spratly Islands. A large number of China Coast Guard vessels were also mobilized.
- Security — Multiple incidents occurred where US and Chinese naval vessels approached within several hundred meters of each other, sharply increasing the risk of accidental collision.
- Diplomacy — There are reports that the US-China military hotline, agreed upon at the APEC Leaders' Meeting in November 2025, has not functioned adequately during actual crisis situations.
- Japan — In response to the South China Sea situation, the Japanese government has strengthened the Japan Maritime Self-Defense Force's surveillance activities. The frequency of destroyer dispatches to the South China Sea has increased.
- Economy — The South China Sea is a vital waterway through which approximately one-third of global maritime trade passes, and escalating tensions directly lead to increased international logistics costs.
- International Law — China has intensified its claims over the "nine-dash line" in the South China Sea, continuing to disregard the 2016 ruling by the Permanent Court of Arbitration.
- Alliance — The Philippines is expanding the rotational deployment of US forces based on the Enhanced Defense Cooperation Agreement (EDCA) updated in 2024.
- Public Opinion — On social media, particularly X, discussions surrounding security policy in Japan have intensified. The pros and cons of increased defense spending and the scope of exercising collective self-defense are points of contention.
- Technology — China is expanding the deployment of DF-26 anti-ship ballistic missiles in its southern coastal regions, strengthening its anti-access/area denial (A2/AD) capabilities against US carrier strike groups.
- Resources — The South China Sea is estimated to hold 11 billion barrels of oil and 190 trillion cubic feet of natural gas, with resource competition also fueling tensions.
- Information — The US Department of Defense's 2025 "Annual Report on China's Military Power" noted that the Chinese Navy's fleet size has exceeded 370 vessels, making it the world's largest navy.
The military confrontation between the US and China in the South China Sea did not suddenly begin in 2026. Its roots trace back to the structural shifts in the balance of power in the Asia-Pacific after the end of the Cold War.
During the Cold War, the South China Sea was relatively stable. Within the framework of US-Soviet rivalry, China had a strong character as a continental power, with limited capacity or will for maritime expansion. However, the collapse of the Soviet Union in 1991 and China's rapid economic growth in the 1990s fundamentally altered this equilibrium. The economic power accumulated under Deng Xiaoping's "tāoguāng yǎnghuì (hide one's capacities and bide one's time)" policy was rapidly converted into military modernization from the 2000s onward.
A turning point was the 2012 Scarborough Shoal incident. China established effective control over Scarborough Shoal after a standoff with the Philippines, demonstrating the prototype of its South China Sea strategy of "accumulating faits accomplis." Subsequently, from 2013 to 2016, China extensively reclaimed seven reefs in the Spratly Islands, constructing artificial islands equipped with runways and radar facilities. This militarization, sometimes called the "Great Wall of Sand," irreversibly changed the power balance in the South China Sea.
In July 2016, the Permanent Court of Arbitration, based on a case filed by the Philippines, issued a landmark ruling that China's claims of historical rights based on the nine-dash line had no legal basis. However, China dismissed this ruling as "a piece of paper" and instead accelerated its militarization. At this moment, the option of resolving disputes through international law was effectively closed, and changing the status quo by force became normalized.
The first Trump administration (2017-2021) significantly increased the frequency of "freedom of navigation operations," ushering in a new phase of military friction between the US and China. The Biden administration (2021-2025) continued this while promoting deterrence against China through strengthening alliance networks, such as the creation of AUKUS (the security framework between Australia, the UK, and the US) and the expansion of EDCA with the Philippines. However, from China's perspective, these moves constituted an "encirclement" and served as justification for countermeasures.
The inauguration of the second Trump administration in 2025 added further uncertainty to this confrontational structure. President Trump's transactional diplomatic style, while showing a tough stance on the Taiwan issue, also carries the potential to use security commitments as a bargaining chip in trade negotiations. This unpredictability itself is a factor of instability in the region.
To understand the situation in early 2026, another structural factor must not be overlooked: the dynamics of China's domestic politics. The Xi Jinping administration faces the paramount task of maintaining domestic cohesion ahead of the 21st Party Congress in 2027. Amidst domestic problems such as slowing economic growth, a prolonged real estate crisis, and persistently high youth unemployment, a tough stance externally serves as a means to bolster the regime's legitimacy. The large-scale military exercises in the South China Sea cannot be understood in isolation from this domestic political context.
Concurrently, the US side also has domestic political drivers. Ahead of the midterm elections in November 2026, a tough stance on China is a theme that easily garners bipartisan support, making it a low-political-cost option for the administration. Thus, the current situation is one where the domestic political dynamics of both countries interact, accelerating the "escalation spiral" in the South China Sea.
For Japan, the South China Sea is not a "distant sea." Approximately 80% of Japan's crude oil imports and most of its LNG imports are transported through sea lanes passing through the South China Sea. Since the establishment of the security legislation in 2015, Japan has put in place a legal framework to commit to the security of the South China Sea through the concept of "situations threatening Japan's survival." The intensification of tensions in 2026 could be the first full-scale test of this framework.
The delta: The essential change in the South China Sea situation in early 2026 is that military exercises by both the US and China have shifted from "demonstrative actions" to a stage of "contact risk." Previous freedom of navigation operations and China's Coast Guard activities were "parallel standoffs" maintaining a certain distance, but with both forces conducting large-scale exercises simultaneously in the same area, the possibility of accidental collision has structurally increased. This change is occurring in an environment where escalation management mechanisms are not functioning, once again exposing the lack of crisis management channels between the US and China, unlike those established by the US and Soviet Union during the Cold War.
🔍 Between the Lines — What the News Isn't Saying
While official statements from both countries champion "freedom of navigation" and "defense of sovereignty," what is unfolding beneath the surface is a resonance between the Xi Jinping administration's domestic signaling, eyeing the 2027 Chinese Communist Party Congress, and the Trump administration's portrayal of a "strong leader" ahead of the 2026 US midterm elections. The overlapping timing of their military exercises is not coincidental; there is a structural need for both sides to have an "external enemy" for domestic consumption. Reports that the US-China military hotline is "not functioning" are likely not because it is genuinely broken, but because it is politically more convenient for both sides if it doesn't function.
NOW PATTERN
Escalation Spiral × Power Overreach × Alliance Strain
The military confrontation between the US and China in the South China Sea exhibits a structural pattern where an "escalation spiral" self-reinforces, and the potential for "power overreach" and "alliance strain" in both countries interact.
Intersection of Dynamics
The three structural patterns—"escalation spiral," "power overreach," and "alliance strain"—do not operate independently but form a complex system that mutually reinforces itself. This intersection is precisely what makes the current situation in the South China Sea particularly dangerous.
As the escalation spiral accelerates, both countries are compelled to commit more military resources to the South China Sea. This exacerbates power overreach. As the costs of overreach increase, the US demands greater burden-sharing from its allies, and China adopts a more assertive posture toward neighboring countries. This deepens alliance strain. When alliance cohesion falters, the credibility of deterrence declines, which in turn triggers further escalation spirals.
Particularly dangerous in this vicious cycle is the problem of "the absence of an exit." To halt the escalation spiral, both sides must simultaneously de-escalate, but domestic political dynamics impede this. To correct power overreach, a reduction in commitments is necessary, but this carries the risk of being perceived as a "sign of weakness." Repairing alliance strain requires time and resources, but the accelerating spiral deprives them of that leeway.
Historically, situations where such complex patterns acted simultaneously—for example, the rigidification of alliance systems and the arms race in pre-World War I Europe—saw the accumulation of rational decisions by individual actors lead to catastrophic outcomes for the entire system. The possibility of the South China Sea in 2026 following this path cannot be ignored. The intersection of these three dynamics means that solving individual problems is insufficient; intervention in the structure itself—that is, the construction of a new regional security architecture—is necessary. However, ironically, now, when the escalation spiral is rotating most intensely, is also the most difficult time for such structural intervention.
📚 Pattern History
1914: The Sarajevo Incident and the Outbreak of World War I
The rigidification of alliance systems and an escalation spiral caused an accidental incident to escalate into a world war. Mobilization plans, believed by each nation to be "defensive," triggered a chain reaction of declarations of war.
Structural similarities with the present: Automatic intervention clauses in alliances and the rigidification of military plans deprive crisis management of options. Flexible crisis communication channels are essential for suppressing the escalation of accidental incidents.
1962: The Cuban Missile Crisis
The US-Soviet standoff, backed by nuclear capabilities, reached the brink of accidental collision. However, leaders on both sides successfully managed to control the escalation, leading to subsequent arms control negotiations and the establishment of a direct telephone line (hotline).
Structural similarities with the present: When a crisis reaches its extreme, direct communication between leaders becomes key to de-escalation. However, this only functions if both sides have the will to "back down."
2001: Hainan Island Incident (EP-3 Incident)
A US Navy EP-3 reconnaissance aircraft and a Chinese J-8 fighter jet collided in mid-air over the South China Sea, resulting in the death of the Chinese pilot. The accidental contact escalated into a diplomatic crisis but was resolved after 11 days of negotiations.
Structural similarities with the present: US-China military contact in the South China Sea is a real risk and has occurred in the past. Resolution requires time and diplomatic channels, and public opinion pressure in the age of social media may reduce that leeway.
2012: Scarborough Shoal Standoff
A maritime standoff between China and the Philippines lasted for several weeks, ultimately resulting in China establishing effective control. The US did not directly intervene, and the Philippines felt "abandoned."
Structural similarities with the present: In great power confrontations, the trust of allies is only substantiated by actual actions. Verbal commitments alone are insufficient as a deterrent.
2023: Intensification of China-Philippines Standoff at Second Thomas Shoal
The China Coast Guard used water cannons against a Philippine military resupply vessel and escalated intimidation tactics, such as shining military-grade lasers. The scope of application of the US-Philippines Mutual Defense Treaty became a focal point.
Structural similarities with the present: Gray zone tactics (actions on the boundary between military and law enforcement) have the effect of gradually escalating conflict while blurring the threshold for full-scale military confrontation.
Patterns Revealed by History
The patterns revealed by historical precedents are consistent. In military confrontations between great powers, individual incidents may appear "manageable," but their accumulation increases structural risk. Like Sarajevo in 1914, the risk of an accidental incident triggering a chain reaction is maximized in an environment where conflict is structured, alliances are rigid, and domestic politics impede de-escalation.
However, the Cuban Missile Crisis of 1962 also shows that catastrophe is not inevitable. If crisis communication channels exist and leaders have the political will, the worst can be avoided. The problem is that the US-China relationship in 2026 is structurally different from the US-Soviet relationship during the Cuban Missile Crisis. The US and Soviet Union shared a common fear of mutually assured destruction (MAD) from nuclear war, but the US-China confrontation in the South China Sea is at the conventional force level, and the brake of "absolute fear of catastrophe" is weaker. Furthermore, social media and the real-time information environment narrow the room for leaders to "save face while making concessions." The EP-3 incident in 2001 was resolved over 11 days, but it is doubtful whether such a time buffer would be available in today's information environment. History simultaneously teaches us the conditions and limits under which crisis management mechanisms function.
🔮 Next Scenarios
Both the US and China will maintain high levels of military tension in the South China Sea throughout 2026, but accidental collisions will be avoided. Both sides recognize that, while maintaining a tough external stance for domestic political reasons, the costs of actual military escalation outweigh the benefits. Specifically, the US Navy will continue to conduct freedom of navigation operations and joint exercises with allies, while China will continue to strengthen military infrastructure on its artificial islands and expand Coast Guard activities. Incidents of close approaches by vessels and aircraft from both forces will continue to occur but will not lead to direct collisions like the 2001 EP-3 incident. Practical-level discussions aimed at improving the operation of the US-China military hotline will take place intermittently. There is a possibility that discussions on a code of conduct for preventing accidental collisions will advance at international forums such as the G20 Leaders' Summit in late 2026. However, no progress will be seen on the South China Sea territorial disputes themselves. Japan will gradually expand the activities of the Japan Maritime Self-Defense Force in the South China Sea while maintaining its response within the framework of the Japan-US alliance. Defense spending increases will continue, but Japan will not engage in direct military action. This state of "managed tension," while unstable, will not immediately lead to catastrophic outcomes.
Implications for Investment/Action: Regular use of US-China military-diplomatic channels. Resumption of substantive discussions on a Code of Conduct (COC) for the South China Sea at ASEAN-related meetings. Signaling by both leaders explicitly stating "avoidance of conflict."
Both the US and China take the risk of accidental collision in the South China Sea seriously and move to establish concrete crisis management mechanisms. For this scenario to materialize, several conditions must align. First, incidents of close approaches by both forces must further intensify in the first half of 2026, leading both leaderships to share the recognition that "control will be lost if things continue this way." Like the US and Soviet Union after the Cuban Missile Crisis, an experience of looking over the "brink" must generate the political will for de-escalation. Concrete outcomes could include a substantive update of the US-China Agreement on Incidents at Sea (INCSEA), establishment of a 24-hour operational system for the military hotline, and agreement on a pre-notification mechanism for military exercises in the South China Sea. ASEAN-led COC negotiations may also progress to discussions on specific draft articles. This scenario is also a favorable development for Japan. The stability of sea lanes would be secured, and Japan could exercise its diplomatic role as a "bridge-builder" between the US and China. However, the probability of this scenario is low because the domestic politics of both the US and China make cooperation difficult. For the Trump administration, rapprochement with China is a political risk, and for the Xi Jinping administration, concessions on issues related to "sovereignty" are unacceptable.
Implications for Investment/Action: Agreement on concrete military confidence-building measures at a US-China summit. China's voluntary reduction in the scale of military exercises in the South China Sea. Decrease in the frequency of US freedom of navigation operations.
An accidental collision occurs between US and Chinese forces in the South China Sea, rapidly deteriorating the regional security environment. In this scenario, a vessel contact incident, an aircraft close-call leading to a crash, or the use of force involving Coast Guard and fishing vessels acts as the trigger. If a collision occurs, the immediate dissemination of information via social media and real-time media will inflame public opinion in both countries, constraining leaders' ability to de-escalate. Nationalist public opinion in China and hardline anti-China sentiment in the US will interact, and the fear of being seen as "weak" will delay resolution. In the worst case, localized armed conflict could occur. While this would not escalate into full-scale war, it would lead to a de facto breakdown of diplomatic relations between the two countries, accelerated economic decoupling, and massive disruption to supply chains. The supply of strategic materials such as semiconductors and rare earths would be cut off, with severe ripple effects on the global economy. Japan would be placed in an extremely difficult position. The dilemma between its obligations under the Japan-US Security Treaty and maintaining economic relations with China would become acute. If the dispatch of the Japan Maritime Self-Defense Force to the South China Sea becomes full-scale, domestic political debate over constitutional interpretation and the application of security legislation will intensify. The risk of spillover into the Taiwan Strait would also sharply increase, destabilizing the entire Indo-Pacific. The impact on markets would also be severe, with crude oil prices soaring (over $100 per barrel), a sharp decline in Asian currencies, and a significant correction in global stock markets.
Implications for Investment/Action: US-China military hotline inoperable. China's unilateral establishment of restricted navigation zones in the South China Sea. Direct use of force against the Philippine military. Dispatch of additional US carrier strike groups.
Key Triggers to Watch
- Disruption or prolonged inoperability of the US-China military hotline: April-June 2026
- China's unilateral declaration of an Air Defense Identification Zone (ADIZ) in the South China Sea: Throughout 2026
- Direct armed conflict between China and the Philippines at Second Thomas Shoal: March-September 2026
- Sharpening of China policy ahead of the US midterm elections in November 2026: July-November 2026
- Decision on foreign policy guidelines at the Plenary Session of the Central Committee of the Communist Party of China: October-December 2026
🔄 Tracking Loop
Next Trigger: ASEAN Regional Forum (ARF) Ministerial Meeting in 2026 (scheduled for July 2026) ── The progress of Code of Conduct (COC) negotiations and whether a bilateral meeting between the US and Chinese foreign ministers materializes will determine the level of tension in the second half of the year.
Continuation of this Pattern: Tracking Theme: South China Sea US-China Military Standoff Escalation Path ── Next milestones are the ARF Ministerial Meeting in July 2026 and military developments around the US midterm elections in November 2026.
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