Where $5.3 trillion in annual trade, contested sovereignty claims, and great-power naval rivalry converge — the South China Sea is the waterway where the Thucydides Trap plays out in real time.
The South China Sea is one of the most strategically consequential bodies of water on the planet. Stretching across roughly 1.4 million square miles between China, Vietnam, the Philippines, Malaysia, Brunei, and Indonesia, it is the maritime crossroads through which roughly one-third of all global shipping passes each year. An estimated $5.3 trillion in trade transits these waters annually, including vast quantities of oil, liquefied natural gas, electronics, and raw materials flowing between East Asia, the Middle East, Europe, and beyond. For China alone, approximately 80 percent of its crude oil imports pass through the South China Sea, primarily via the narrow Strait of Malacca at its southern edge.
Beyond trade, the South China Sea is believed to contain enormous reserves of untapped natural resources. Geological surveys estimate that the seabed holds approximately 11 billion barrels of oil and 190 trillion cubic feet of natural gas — stakes that would be significant for any country but are especially consequential for the energy-hungry economies that ring these waters. Rich fishing grounds sustain millions of livelihoods across Southeast Asia, generating an estimated $21 billion in annual catches. For nations like Vietnam and the Philippines, these fisheries are not economic abstractions; they are matters of food security and rural survival.
Strategically, the South China Sea occupies a position of extraordinary importance in the broader architecture of Indo-Pacific security. It is bordered by the Strait of Malacca to the southwest and the Luzon Strait to the northeast — two of the world's most critical maritime chokepoints. Control of these waters would confer enormous leverage over the flow of energy and commerce to Japan, South Korea, and Taiwan, all of which depend on unimpeded passage through the South China Sea for their economic survival. In the context of the Thucydides Trap, the South China Sea is not merely a dispute over rocks and reefs. It is a contest over the control of the maritime commons that underpins the entire global economic order.
"The South China Sea is to the 21st-century US-China rivalry what the North Sea was to the Anglo-German rivalry before World War I — a body of water where strategic ambitions, economic interests, and national pride collide with no easy path to compromise."
At the heart of the South China Sea dispute lies China's "nine-dash line" — a sweeping cartographic claim that encompasses approximately 90 percent of the South China Sea, extending hundreds of miles from the Chinese mainland and overlapping with the exclusive economic zones of Vietnam, the Philippines, Malaysia, Brunei, and Indonesia. First published on a map by the Republic of China in 1947 and subsequently adopted by the People's Republic, the nine-dash line has never been precisely defined in legal terms. Beijing has deliberately maintained ambiguity about whether the line represents a claim to the islands within it, to the waters themselves, or to some combination of both. What is clear is that China asserts "indisputable sovereignty" over virtually all the features — islands, reefs, shoals, and atolls — enclosed by the line.
Beginning around 2013, China embarked on one of the most audacious engineering projects in modern military history: the large-scale construction of artificial islands atop submerged reefs and shoals in the Spratly and Paracel island chains. Using fleets of dredging vessels, China transformed tiny coral features — many of which were barely above water at high tide — into substantial artificial islands, creating an estimated 3,200 acres of new land. On these manufactured territories, China has built military-grade airstrips capable of handling fighter jets and heavy transport aircraft, deep-water harbors, radar installations, surface-to-air missile batteries, anti-ship cruise missile systems, barracks, and communications facilities.
The most heavily fortified of these artificial islands — Fiery Cross Reef, Subi Reef, and Mischief Reef — have been transformed into what military analysts describe as "unsinkable aircraft carriers." Together, they give China a network of forward-deployed military bases deep in the South China Sea, extending its power-projection capability hundreds of miles beyond its coastline. These installations enable China to establish effective air and sea control over vast stretches of contested water, complicating the operations of any rival military force and reinforcing Beijing's sovereignty claims through sheer physical presence.
China's island-building campaign was conducted in defiance of repeated protests from neighboring countries and the United States, and it illustrates a pattern central to the Thucydides Trap dynamic: a rising power using its growing capabilities to alter the status quo in its favor, creating facts on the ground — or in this case, on the water — that are difficult to reverse without the use of force. Each new runway, each new missile battery, shifts the strategic balance incrementally in Beijing's favor, while making the cost of any future challenge progressively higher.
"China's island-building is not construction. It is the physical manifestation of a sovereignty claim — concrete and steel poured over coral reefs to create irreversible strategic facts in the heart of contested waters."
The United States' primary tool for challenging China's expansive claims in the South China Sea is the Freedom of Navigation Operations program, known by the acronym FONOPs. These are deliberate transits by US Navy warships through waters that China claims as its own but that the United States considers international waters open to all nations under the United Nations Convention on the Law of the Sea (UNCLOS). The US has conducted FONOPs in the South China Sea with increasing frequency since 2015, sailing guided-missile destroyers and cruisers within 12 nautical miles of China's artificial islands to demonstrate that the United States does not recognize Chinese sovereignty over these features.
FONOPs are not acts of aggression. They are, at their core, legal assertions — physical demonstrations that the United States rejects excessive maritime claims that would restrict the freedom of navigation upon which the global economy depends. The principle is straightforward: if international waterways are allowed to be claimed by coastal states without challenge, the cumulative effect would be a fragmentation of the maritime commons that would undermine the free movement of goods, energy, and naval forces worldwide. For the United States, whose global power-projection capability depends on unimpeded naval access, the principle of freedom of navigation is not abstract. It is existential.
But FONOPs also carry inherent risks. Each transit brings US warships into close proximity with Chinese naval vessels, coast guard cutters, and maritime militia boats that are tasked with asserting Chinese sovereignty. Close encounters between American and Chinese ships and aircraft have become increasingly common and increasingly dangerous. In 2018, a Chinese destroyer came within 45 yards of the USS Decatur in the South China Sea, forcing the American ship to maneuver to avoid a collision. In 2023, a Chinese fighter jet conducted an "unsafe intercept" of a US reconnaissance aircraft, passing within 400 feet at high speed. These incidents are not isolated; they are part of a pattern of escalating encounters that raises the specter of an accidental collision, a miscalculated response, or a crisis that neither side intended but neither side can control.
The dilemma for Washington is recursive. If the US stops conducting FONOPs, it effectively acquiesces to China's claims, setting a precedent that could embolden further territorial expansion and undermine the rules-based maritime order. If it continues, it risks a confrontation that could escalate from a minor naval incident to a crisis with global consequences. This is the strategic treadmill that defines great-power competition in the South China Sea — a dynamic where maintaining the status quo requires continuous risk-taking, and where each cycle of challenge and response ratchets the tension incrementally higher.
The South China Sea dispute is often framed as a bilateral US-China confrontation, but the reality is far more complex. At least four ASEAN member states — the Philippines, Vietnam, Malaysia, and Brunei — maintain their own overlapping territorial claims in the South China Sea, and each faces its own agonizing calculations about how to navigate the great-power rivalry unfolding in their waters. These nations are not passive spectators; they are claimants with vital economic, security, and sovereign interests at stake, trapped between a rising regional hegemon and a distant superpower whose commitment to the region is perpetually in question.
The Philippines occupies the most precarious position among the ASEAN claimants. As the only Southeast Asian nation with a formal mutual defense treaty with the United States, Manila has the most explicit security guarantee — but also the most direct exposure to Chinese pressure. The standoff at Second Thomas Shoal, where a small contingent of Philippine Marines lives aboard a deliberately grounded World War II-era ship, the BRP Sierra Madre, has become one of the most visible and volatile friction points in the South China Sea. Chinese coast guard vessels routinely block Philippine resupply missions, using water cannons, laser devices, and physical obstruction to prevent food and supplies from reaching the Marines. Each resupply run carries the risk of an incident that could invoke the US-Philippines Mutual Defense Treaty and draw Washington into a direct confrontation with Beijing.
Vietnam, which has fought actual wars with China over South China Sea territory, maintains the second-largest number of occupied features in the Spratlys and has invested heavily in its naval and air defense capabilities. Hanoi walks a delicate line — building closer military ties with the United States, India, and Japan while maintaining a formal partnership with Beijing and avoiding actions that would force it to choose sides explicitly. Malaysia, meanwhile, has faced growing Chinese incursions into waters near its oil and gas operations off Sarawak and Sabah, yet has generally preferred quiet diplomacy over public confrontation.
For all of these nations, the central dilemma is the same: they are too small to resist Chinese pressure individually, too divided to present a unified front collectively, and too uncertain of American staying power to rely exclusively on Washington. The ASEAN consensus model — which requires unanimity for joint action — has repeatedly been exploited by China, which has used its economic leverage over Cambodia and Laos to block any ASEAN statement that directly challenges Beijing's claims. The result is a strategic fragmentation that serves China's interests: each claimant is isolated, each bilateral dispute is manageable, and the collective pressure that might constrain Chinese behavior never materializes.
On July 12, 2016, the Permanent Court of Arbitration in The Hague issued a landmark ruling in a case brought by the Philippines against China under the United Nations Convention on the Law of the Sea. The tribunal's decision was sweeping and unambiguous: China's nine-dash line had no legal basis under international law. The court found that China had no historical rights to resources in the South China Sea beyond those provided by UNCLOS, that several features China had claimed as islands — which would generate their own exclusive economic zones — were legally only rocks or low-tide elevations entitled to no such zones, and that China had violated the Philippines' sovereign rights by interfering with fishing and petroleum exploration within the Philippines' exclusive economic zone.
The ruling was the most significant legal challenge ever mounted against China's South China Sea claims, and it represented a potential turning point in the dispute. If China had accepted the ruling, it would have established a legal framework for resolving overlapping claims peacefully and would have significantly constrained Beijing's freedom of action in the region. Instead, China rejected the ruling entirely. Beijing declared it "null and void" and "without binding force," refused to participate in the proceedings, and continued its island-building and military operations unabated. Chinese state media described the ruling as a political instrument of Western powers designed to contain China's rise.
China's rejection of the Hague ruling carries implications that extend far beyond the South China Sea. It represents a direct challenge to the rules-based international order that the United States and its allies have maintained since the end of World War II. If the largest rising power in the international system can dismiss the rulings of an international tribunal without consequence, the precedent undermines the entire architecture of international law — a prospect that alarms not only the claimant states in the South China Sea but also nations worldwide that depend on the rules-based order for their security. In the framework of the Thucydides Trap, China's defiance echoes a recurring pattern: rising powers that have outgrown the existing international order refuse to be constrained by rules they had no role in creating, while ruling powers insist on those rules precisely because they underpin the status quo that favors them.
"China's rejection of the Hague ruling was not merely a legal dispute. It was a declaration that the existing rules-based order is insufficient for a rising great power — a posture that, historically, has been among the most reliable precursors to systemic conflict."
The dynamics unfolding in the South China Sea have unmistakable parallels to previous episodes of maritime competition between rising and ruling powers — episodes that, more often than not, ended in conflict. The most instructive parallel is the Anglo-German naval rivalry of the late 19th and early 20th centuries, a competition that was both a symptom of the broader Thucydides Trap between Britain and Germany and a direct accelerant of the tensions that produced World War I.
In the 1890s, Kaiser Wilhelm II and Admiral Alfred von Tirpitz embarked on an ambitious naval building program designed to challenge Britain's dominance of the seas. Germany's High Seas Fleet was not built for a specific military objective; it was built to alter the strategic balance, to give Germany the leverage that comes with the ability to threaten a ruling power's most vital interest. For Britain, which depended on naval supremacy for the security of its global empire and the protection of its trade routes, the German naval buildup was an existential threat. London responded with its own massive building program, culminating in the revolutionary HMS Dreadnought class of battleships. The result was a classic arms race that consumed enormous resources on both sides, poisoned diplomatic relations, and created a climate of mutual suspicion in which compromise became politically impossible.
The parallel to the South China Sea is striking. China's naval expansion — which has seen the PLA Navy grow from a coastal defense force to the world's largest navy by number of vessels in barely two decades — serves a similar structural function. It is designed to challenge the United States' command of the maritime commons in the Western Pacific, the foundation of American strategic dominance in Asia. The United States, like Britain before it, views this challenge as a threat to the system upon which its security and that of its allies depends. Washington has responded with its own military investments, forward deployments, and alliance-building — a counter-buildup that mirrors London's response to Tirpitz's fleet.
Another historical parallel lies in the Mediterranean rivalries of the early 20th century, where France, Italy, and Austria-Hungary competed for influence in a semi-enclosed sea bordered by multiple powers with overlapping claims. The Mediterranean, like the South China Sea today, was simultaneously a vital trade route, a zone of colonial competition, and a space where naval demonstrations served as proxies for broader strategic ambitions. The interlocking alliance commitments that developed around Mediterranean rivalries helped transform what might have been regional disputes into triggers for a continental war.
What these historical parallels reveal is a structural pattern: when a rising maritime power challenges a ruling maritime power's control of strategically vital waters, the result is almost always an escalating cycle of military buildup, provocative demonstrations, and hardening political positions that makes peaceful resolution progressively more difficult. The South China Sea today exhibits every element of this pattern. The question is whether the United States and China can break the cycle before it reaches its historical conclusion.
The South China Sea is dangerous not because either the United States or China wants a war over reefs and shoals, but because the density of military assets, the frequency of close encounters, and the absence of reliable de-escalation mechanisms create conditions in which an unintended incident could spiral out of control. Understanding the most plausible escalation scenarios is essential for assessing the real level of risk.
The most likely trigger for a South China Sea crisis is the one that requires the least strategic intent: an accidental collision between American and Chinese naval vessels or aircraft during a routine encounter. US and Chinese ships and aircraft operate in close proximity on a near-daily basis. The historical record is full of near-misses — the 2001 EP-3 incident, in which a Chinese fighter jet collided with a US reconnaissance aircraft and forced an emergency landing on Hainan Island, demonstrated how quickly an airborne accident can become an international crisis. In the current environment, where both sides have larger and more capable forces operating in closer quarters, the probability of a similar or more serious incident has increased substantially. A collision that results in casualties could generate intense domestic pressure on both sides to respond forcefully, creating an escalation dynamic that political leaders may struggle to control.
China's maritime militia — a fleet of ostensibly civilian fishing vessels that operate under the direction of the PLA and the Chinese coast guard — adds a uniquely destabilizing dimension to the South China Sea. These vessels regularly swarm contested features, obstruct the fishing operations of other nations' boats, and support Chinese sovereignty claims through sheer physical presence. A confrontation between Chinese militia vessels and Philippine, Vietnamese, or other ASEAN fishing boats could escalate quickly, especially if a claimant nation's navy intervenes to protect its citizens. The involvement of a US treaty ally — particularly the Philippines — could draw Washington into a crisis that begins as a fisheries dispute and ends as a great-power confrontation.
The most severe escalation scenario short of outright war would be a Chinese declaration of an Air Defense Identification Zone (ADIZ) over the South China Sea or the establishment of a military exclusion zone around its artificial islands. China declared an ADIZ over the East China Sea in 2013 — a move that the United States promptly challenged by flying B-52 bombers through it — and has been widely expected to eventually do the same in the South China Sea. Such a declaration would force the United States and its allies to choose between compliance, which would effectively recognize Chinese dominance over the region, and defiance, which would risk a military confrontation. A blockade of specific features, such as the Philippines' outpost at Second Thomas Shoal, would present an even starker choice: intervene militarily or watch a treaty ally be coerced into submission.
"The danger in the South China Sea is not a bolt-from-the-blue attack. It is the slow accumulation of incidents, each manageable on its own, that collectively erode the guardrails until a single miscalculation triggers a crisis that neither side can walk back."
If the structural dynamics of the Thucydides Trap make the South China Sea inherently prone to escalation, are there mechanisms that can prevent the dispute from tipping into open conflict? The answer is uncertain, but several diplomatic and institutional pathways offer at least the possibility of managing the risks, even if they cannot resolve the underlying tensions.
The ASEAN-China Code of Conduct negotiations represent the most prominent diplomatic effort to establish rules of the road in the South China Sea. Negotiations on a binding Code of Conduct began formally in 2017, building on a non-binding Declaration on the Conduct of Parties signed in 2002. Progress has been glacially slow. More than two decades after the original declaration, the parties have yet to agree on fundamental questions: whether the code will be legally binding, whether it will cover all of the South China Sea or only specific areas, and whether it will include enforcement mechanisms. China has generally favored a weaker, non-binding framework — one that constrains the behavior of external powers (read: the United States) while preserving Beijing's own freedom of action. ASEAN claimant states, particularly the Philippines and Vietnam, have pushed for a stronger, legally binding agreement. The gap remains wide, and many analysts are skeptical that a meaningful code will be concluded in the foreseeable future.
Bilateral hotlines and crisis communication protocols between the US and Chinese militaries are essential for preventing incidents from escalating. The two militaries have established several communication mechanisms, including the Military Maritime Consultative Agreement and various memoranda of understanding on encounters at sea and in the air. But these mechanisms have proven unreliable in practice. China has periodically suspended military-to-military communications as a form of political signaling, precisely during the moments when such communication is most needed. Ensuring that crisis communication channels remain open and functional regardless of the political climate is a prerequisite for managing the risk of accidental escalation.
Multilateral cooperation on non-traditional security issues — environmental protection, marine scientific research, search and rescue, and counter-piracy operations — offers a potential avenue for building habits of cooperation in the South China Sea. Functional cooperation on issues of mutual interest can create institutional links, personal relationships, and norms of behavior that make conflict marginally less likely. These are incremental measures, not transformative solutions, but in a situation where the fundamental political disputes are intractable, incremental risk reduction may be the best available option.
Diversifying energy supply chains and trade routes can reduce the strategic stakes of the South China Sea over the long term. If China reduces its dependence on oil imports transiting the Strait of Malacca through pipeline construction, renewable energy investment, and strategic petroleum reserves, the existential dimension of its South China Sea claims may soften. Similarly, if ASEAN nations develop alternative economic partnerships that reduce their dependence on Chinese trade, they may gain greater freedom to resist Chinese pressure. These are long-term structural shifts, not immediate solutions, but they can alter the incentive landscape in ways that make compromise more feasible.
Ultimately, managing the South China Sea requires recognizing a difficult truth: the underlying sovereignty disputes are almost certainly irresolvable in the near term. No Chinese leader will abandon the nine-dash line, and no ASEAN claimant will renounce its own claims. The goal, then, is not resolution but management — creating enough guardrails, communication channels, and mutual restraints to ensure that the competition remains below the threshold of armed conflict. History suggests this is possible but difficult. The four Thucydides Trap cases that ended without war required sustained diplomatic engagement, mutual restraint, and leaders willing to absorb domestic political costs in the interest of avoiding catastrophe. Whether the nations contesting the South China Sea can summon similar statesmanship remains the defining question of this maritime flashpoint.
"The South China Sea cannot be solved. It can only be managed. And the margin between management and miscalculation grows thinner with every passing year."