When imagining how the U.S.-China relationship might devolve into war, experts often cite Taiwan as the most obvious flashpoint. In recent years, after all, China has escalated its campaign of coercion against the island democracy, lobbing missiles over it, staging a blockade during live-fire military exercises, and threatening catastrophic punishments against third countries that expand ties with Taipei. Although the United States does not have a defense treaty with Taiwan, Beijing’s aggression against the island—paired with Chinese President Xi Jinping’s reported desire to be capable of invading by 2027—has prompted the U.S. military and policy community to accelerate steps that would strengthen cross-strait deterrence.
But if conflict does break out in the Western Pacific, it is more likely to erupt southwest of Taiwan, in the South China Sea, where numerous countries jostle over competing maritime claims and divergent visions of sovereignty, regional order, and international law. Beijing claims about 90 percent of the South China Sea, including waters off the coasts of Brunei, Indonesia, Malaysia, the Philippines, and Vietnam. Those five countries’ maritime claims—and Taiwan’s—also conflict with one another, but China’s claims and actions have been far more aggressive, including deployments of hundreds of ships, advanced missile systems, and combat aircraft to the coral reefs, rocks, and cays it occupies.
Tensions are highest between China and the Philippines, with Manila frequently calling public attention to Chinese harassment of Philippine ships operating lawfully within the Philippines’ exclusive economic zone. But violence also erupts periodically between China and other claimants. Since 2015, Chinese coast guard, militia, and civilian maritime personnel have killed or injured dozens of Vietnamese fishermen in the South China Sea. And in the 2010s, the Indonesian government routinely destroyed trespassing vessels from China and other countries. U.S. ships and aircraft, meanwhile, operate throughout the South China Sea, challenging Beijing’s expansive claims, affirming freedom of navigation and overflight, and helping Southeast Asian claimants withstand Chinese harassment.
No one wants to fight a war over an obscure set of rocks in the South China Sea. There will never be a U.S. president who is eager to convince the American people that defending freedom of navigation in Asia merits a great-power conflict. China would prefer to reserve its military capabilities for a potential scenario in Taiwan. Even in Manila or Hanoi, where upholding maritime sovereignty is a winning political issue, there is a strong preference for maintaining warm economic ties with China. Nonetheless, the risk that an accident in the South China Sea could rapidly escalate to a full-blown crisis remains substantial.
Washington has a legally binding alliance commitment to the Philippines. The U.S.-Philippine Mutual Defense Treaty of 1951 does not mention the South China Sea, referring instead to “the Pacific Area.” But since 2019, the United States has explicitly included the South China Sea as part of that geography, formally guaranteeing the Philippines’ security there. The White House, Department of State, and Department of Defense have repeatedly confirmed that an armed attack against Philippine armed forces, public vessels, or aircraft in the South China Sea would invoke U.S. mutual defense obligations. In a rare point of continuity, both Trump administrations and the Biden administration have used nearly identical language to underscore this commitment. As a result, if China kills a Philippine service member, even inadvertently, in the South China Sea, the United States could easily become a party to the conflict.
The United States, of course, could choose to abandon the alliance instead. It might judge that defending U.S. interests in the South China Sea is simply not worth the risk. Undoubtedly, the importance of these waters would seem to pale in comparison to Taiwan, a densely populated democracy and technological hub. But since 2019, Washington has been remarkably consistent in supporting Manila when it comes under pressure in the South China Sea, often offering even more assistance than the Philippines had requested. For Washington, standing up for Manila in the South China Sea is important in its own right. But it is also necessary for a successful defense of Taiwan. Only 53 nautical miles separate the Philippines from Taiwan at their closest point. In a cross-strait conflict, U.S. officials would depend on Philippine cooperation—and the United States can only retain Philippine support on Taiwan if they deliver for Manila in the South China Sea. If Washington blinks in the South China Sea, in other words, its ability to deter China in the Taiwan Strait could be fatally undermined.
BLOOD IN THE WATER
Of the United States’s36 treaty allies, the only country that has taken casualties from China since the Korean War is the Philippines. In 2023, Beijing launched a fierce campaign against Philippine ships in the South China Sea, setting in motion a conflict that brought the United States and China to the brink of military confrontation. Chinese coast guard vessels rammed and fired water cannons at civilian Philippine ships seeking to resupply the Philippines’ outpost at Second Thomas Shoal, a feature that falls within the Philippines’ exclusive economic zone. The danger peaked in June 2024, when Chinese coast guard personnel wielded axes and knives against Philippine mariners, one of whom lost a thumb in the skirmish.
Throughout the crisis, the United States made clear that it would defend its treaty ally. Admiral Samuel Paparo, the commander of U.S. Indo-Pacific Command, noted that it would be “an entirely reasonable option” for U.S. ships to escort Philippine vessels in the contested area. China pulled back from the precipice, reaching a “provisional arrangement” with the Philippines under which the latter’s resupply missions to Second Thomas Shoal would be monitored but not attacked. Yet the Chinese coast guard has continued to attack Philippine ships elsewhere within Philippine waters, more than 500 nautical miles from the Chinese coast.
The Philippines is not the only U.S. ally at risk in the South China Sea. Australia, Japan, and NATO countries fly and sail through areas claimed by Beijing, and Chinese aircraft and vessels have used dangerous maneuvers to oppose their presence. In October 2025, for example, a Chinese fighter jet released flares in close proximity to an Australian P-8A aircraft traversing the Paracel Islands. A crash or collision resulting from these unsafe interactions could swiftly devolve into a significant crisis, especially since there are no effective channels for crisis management or real-time de-escalation.
NO ONE PICKS UP
Military-to-military communication between the United States and China is limited in the best of times and often evaporates at the beginning of a crisis. These channels will be even less useful amid Xi’s ongoing purges of senior officers in the People’s Liberation Army (PLA). It seems unlikely that a PLA officer would take the political risk of speaking to the U.S. military without explicit instructions, which can take days or weeks to arrive. Communication channels between China and the Philippines are worse still. The two countries have launched numerous hotlines intended to manage tensions in the South China Sea. But when the Philippines tries to use them, no one picks up. Vietnam can use Communist Party channels to smooth tensions with China over the longer term, but existing hotlines for crisis management are likewise unreliable.
Adding to these difficulties, the South China Sea lacks widely understood rules for de-escalation or conflict avoidance. By contrast, China, Taiwan, and the United States have navigated numerous crises in the Taiwan Strait and have stewarded a contested status quo through eight decades of tensions. In doing so, they have established a kind of scaffolding for de-escalation or, at a minimum, efforts to avoid catastrophic misunderstandings. In Washington, for example, tensions around Taiwan are circumscribed by the provisions of the Taiwan Relations Act, three joint communiques with Beijing, and six assurances to Taiwan. Informal understandings such as the “Davis Line,” which divides the Taiwan Strait in two with the expectation Taipei and Beijing will stay on their respective side, are now routinely violated by Beijing. But the line remains relevant, as observers still measure Beijing’s crossings to ascertain its mood towards Taiwan. The South China Sea has no such architecture, with one exception: the Declaration on the Conduct of Parties in the South China Sea (DOC).
The risk that an accident in the South China Sea could escalate to a crisis is substantial.
The DOC represents one of the most significant achievements of the Association of Southeast Asian Nations (ASEAN). Signed by the Southeast Asian countries and China in 2002, the DOC effectively froze the status quo, establishing an understanding that claimants would not seize South China Sea outposts from one another—and that unoccupied features would be left undisturbed. For two decades, Beijing appeared to accept this normative framework. But in 2023, when China launched its increasingly violent campaign at Second Thomas Shoal, the Chinese leadership demonstrated a more revisionist approach, insisting that the Philippines’ presence, which dates to 1999, was not part of the status quo, and backing that position with near-lethal force. Last October, China rammed a Philippine ship approaching Thitu Island, which the Philippines has occupied since 1971 and which remains Manila’s primary outpost in the South China Sea. Beijing insisted that the Philippines “took infringement and provocative activities first” and described its ramming as “legitimate and lawful measures” required to “defend its sovereignty.”
Additionally, in late 2022, Bloomberg reported that China was artificially expanding unoccupied features throughout the Spratly archipelago. China was evidently trying to hide its fingerprints, moving sand in small quantities in a manner the U.S. Department of Defense has characterized as “covert.” Beijing has categorically denied that it is doing any of this, indicating that China recognizes its actions are inconsistent with acceptable practice. This erosion of DOC norms suggests that the only rules that have successfully reduced the risk of conflict in the South China Sea may be gradually losing sway.
ASEAN, meanwhile, has found itself trapped in a feckless neutrality, neither acquiescing to Beijing completely nor supporting its members when China attacks. When the Chinese coast guard used axes to attack a civilian Philippine ship within the Philippines’ exclusive economic zone, ASEAN could not even muster a statement of concern.
GATHERING STORMS
For more than two decades, ASEAN and Beijing have been trying to negotiate a Code of Conduct (CoC) for the South China Sea, a document that would operationalize the 2002 DOC’s principles and establish clear, enforceable rules to limit the risk of escalation. Every year a new ASEAN country takes over the body’s rotating chairmanship, and every year the chair insists that they will complete the CoC. But talks remain at an impasse thanks to China’s efforts to sideline the UN Convention on the Law of the Sea (UNCLOS), under which China’s expansive maritime claims are unlawful.
China hopes that a favorable set of CoC rules will supersede UNCLOS, providing Beijing with firmer ground from which to assert its purported “historical rights.” ASEAN countries know that UNCLOS is on their side, and they will not surrender the moral high ground it provides. China has also tried to circumscribe the rights of third parties such as the United States, insisting that disputes in the South China Sea should be managed by CoC signatories and no one else. ASEAN countries’ maritime capacity is exceedingly limited compared to that of China, and they rely on the United States and other external powers to deter Beijing. Because China will not soften its demands, a credible CoC will remain out of reach.
More informal diplomatic tools are also falling short. In the past, Southeast Asian claimants could reliably prompt a tactical Chinese retreat by drawing public attention to Beijing’s acts of aggression. China was sensitive to the reputational cost of appearing to bully its neighbors. But starting in late 2023, this time-tested strategy began to fail. Instead, China fought back with its own information campaigns, escalating tensions rather than smoothing them over. As long as viable diplomatic options for de-escalation remain out of reach, the risk of an inadvertent crisis will increase.
Paradoxically, the risk of escalation may be higher because the immediate stakes appear lower. Notwithstanding the military, commercial, and environmental significance of the South China Sea, many of the disputes concern barely inhabited rocks in the middle of the ocean. In contrast to Taiwan, which is home to 23 million people and most of the world’s advanced semiconductor manufacturing, the South China Sea appears to be a relatively safe space for signaling uncompromising resolve, burnishing nationalist credentials, and demonstrating credibility to allies. This leads all sides to exercise less caution and accept more risk. The Chinese coast guard does not wield axes at mariners in the Taiwan Strait. But at Second Thomas Shoal, they deemed that to be a reasonable mode of communication. At the same time, the United States has felt comfortable extending increasingly precise security guarantees to the Philippines in disputed areas.
As time passes, the risk profile of the South China Sea will only become more complex. The South China Sea, for example, is a busy throughway for the subsea cables that serve as the backbone of the modern Internet—yet China rarely allows foreign providers to repair the cables there, and these thin optical fibers are tremendously vulnerable to sabotage. In 2025, China dramatically expanded its operations around Pratas Island, one of Taiwan’s long-standing outposts in the South China Sea, creating a dangerous new flashpoint that combines the complex risk profile of the Taiwan Strait and the South China Sea. Meanwhile, as Russia has grown increasingly dependent on China for the economic and military support that sustains its war against Ukraine, Moscow has steadily abandoned long-standing policies that were intended to preserve a relative advantage vis-à-vis Beijing, including endorsing a broader role for China in Central Asia, offering China greater access to the Arctic, and sharing sensitive military technology with the PLA. If the war in Ukraine continues, Moscow may discard its modestly pro-Vietnam position in the South China Sea and endorse China’s maritime claims, with potentially destabilizing consequences. The waterway’s balance of power is already fragile; Russia’s support of China there could embolden Beijing to use more violent tactics and more brazenly disregard international law.
CHARTING A NEW COURSE
If the United States wishes to lessen the risk of war in the South China Sea, it can choose between two approaches. The first would be to accept China’s expansive claims. If Washington were to strike a deal along these lines, the Southeast Asian claimants may conclude that they have no choice but to follow suit, reducing the likelihood of near-term confrontation. But this could result in significant interference with maritime commerce, as China would have a free hand in disrupting freedom of navigation in this critical waterway, through which one-third of global trade now passes. It would also shatter the credibility of U.S. alliance commitments, cast the defense of Taiwan in a highly implausible light, and signal a broader American decline, likely catalyzing other conflicts around the world. Even if China offers concessions in return, these would most likely be tactical economic gestures, such as the agricultural purchase commitments that are favored by the Trump administration, and would do nothing to offset strategic fallout. China might promise to be a responsible steward of the South China Sea and respect third countries’ rights in the absence of U.S. intervention. But in 2015, China promised that it would not militarize its South China Sea outposts and then violated this pledge almost immediately.
The more sensible path requires Washington to strengthen deterrence in the South China Sea, while striving for clear communication with Beijing regarding each side’s redlines. To achieve this, the United States should prioritize support for its Southeast Asian partners, helping them resist Chinese aggression and uphold their sovereign rights. Washington can help them develop low-cost defense capabilities, such as aerial and maritime drones that can counter China’s gray-zone coercion and its superior maritime forces. At the same time, Washington must support its partners’ basic capacity to patrol their own waters; it should transfer more naval and Coast Guard ships to these partners, provide fuel to facilitate longer patrols, and share data that will enhance their real-time awareness of Chinese incursions. The United States can also facilitate greater unity among the coastal ASEAN countries, which can more ably contribute to regional deterrence when they stand together. For example, Washington should actively encourage the speedy resolution of maritime disputes between Southeast Asian countries, which can otherwise distract from the more difficult challenge of deterring Beijing. The United States should also ramp up capacity-building programs for the maritime law enforcement agencies of Southeast Asia, fostering interoperability among these forces along the way.
Most importantly, the United States should strengthen its alliance with the Philippines. Beyond the military relationship, Washington should help Manila address any vulnerabilities that China could weaponize to gain leverage in the South China Sea. For example, the United States must partner with the Philippines to solve its looming energy crisis. The natural gas reserves on which Manila depends for its electricity will be depleted within the next several years, and the government has not yet developed an adequate plan for closing the gap in its energy supplies. If no solution is identified, Beijing could force Manila to endorse Chinese sovereignty over the South China Sea in exchange for desperately needed offshore drilling rights. The precarious state of Philippine energy security was clearly illustrated in March, when Philippine President Ferdinand Marcos Jr. declared a national state of emergency due to Iran’s closure of the Strait of Hormuz. A week later, for lack of better options, Marcos stated he was newly open to partnering with China on energy exploration in the South China Sea.
The United States should help its Southeast Asian partners resist Chinese aggression.
The United States can also support deterrence by internationalizing the South China Sea. By encouraging European and Indo-Pacific maritime forces to sail and fly through the South China Sea at every opportunity and to undertake joint exercises and patrols with ASEAN countries, Washington can raise the costs of escalation beyond what Beijing is willing to pay, while also signaling to the Southeast Asian claimants that the world is on their side, thereby strengthening their resolve. Deepening the U.S.-Japanese-Philippine maritime partnership, including through an enhanced program of Coast Guard exercises, will be essential. Washington should also work to build international consensus behind the 2016 ruling of the UNCLOS arbitral tribunal—which found the vast majority of China’s claims to be unlawful.
Likewise, the United States should consistently raise the importance of the South China Sea in meetings with Xi and other Chinese officials, as well as urge other governments to do the same. Xi is not seeking a war in the South China Sea, but his forces often appear to significantly underestimate the risk they are incurring. To correctly appraise the risk of escalation, Xi and his lieutenants must understand that powerful countries around the world do not view the South China Sea as an internal affair of China.
In these exchanges, Washington should communicate clear redlines to Beijing. In a moment of crisis, effective communication will be exceedingly difficult. But over a longer horizon, there are opportunities for meaningful bilateral diplomacy. Ultimately, China hopes to prevent the United States from becoming more involved in the South China Sea. Beijing seeks to advance its claims as far as possible, while staying just short of a threshold that would trigger more serious U.S. engagement. It is critical for Washington to help the Chinese leadership understand where that threshold lies, and it cannot rely on the existing military-to-military channels to achieve this. Clear communication between adversaries may be one of diplomacy’s most difficult tasks, but in the South China Sea it could make the difference between war and peace.
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