In April 2025, Chinese coast guard personnel stepped onto Sandy Cay, an uninhabited sandbar in the Spratly Islands in the South China Sea, and unfurled the Chinese flag. In much of the world, this act passed almost unnoticed. But as China’s first formal, on-the-ground assertion of sovereignty over an unoccupied land feature in more than a decade, it signaled a broader shift in Beijing’s quest for control: China is again contesting disputed land features, after years in which disputes over rights at sea have been the primary source of conflict.

Beijing’s targeting of unoccupied features, which is not limited to Sandy Cay, reflects an important change since its last major island-building campaign. Between late 2013 and 2015, when the bulk of that work took place, China dredged sand and coral to enlarge seven features it already occupied, later constructing military and civilian facilities on them. By extending its activities to uninhabited features, Beijing is straining a 2002 nonbinding commitment it made with the members of the Association of Southeast Asian Nations (ASEAN) not to inhabit them. Meanwhile, Beijing continues to challenge its neighbors’ exercise of sovereign rights at sea, interfering with fishing and offshore energy activity and conducting unauthorized marine surveys in their exclusive economic zones.

Beijing’s methods have been shifting, too, with high-intensity incidents becoming less frequent, although clashes this month suggest that the decline may not endure. Between February 2023 and July 2024, Chinese coast guard and maritime militia vessels often used military-grade lasers and water cannons, carried out dangerous maneuvers, and rammed vessels to obstruct Philippine resupply missions, patrols, and fishing. The lull through the first half of this year may partly have reflected Manila’s decision, as chair of ASEAN, to moderate its policy of “radical transparency,” the systematic public exposure of unlawful and coercive Chinese acts at sea. The broader easing, however, likely reflected Beijing’s choice to reduce head-on confrontations, even as it advanced its claims through large-scale infrastructure projects and quieter activities such as conducting marine scientific research, symbolically asserting sovereignty over land, and placing temporary floating structures at or near disputed features.

Individually, China’s quieter acts might seem inconsequential. Collectively, they could alter the strategic landscape. They complicate the calculus of coastal states, which may judge any single Chinese move to be too minor to justify a response that risks escalation. That concern weighs especially heavily as these states face the fallout from the war in the Middle East and sweeping U.S. tariffs, pressures that may force many of them to recalibrate their relationships with Beijing. China’s strategy of consolidating and normalizing control at sea and on land threatens to erode the regional order and weaken the rule of law. Its quieter measures also threaten a key element of U.S. regional strategy. Washington has relied on exposing Beijing’s unlawful and coercive conduct to rally allies and partners behind efforts to uphold the law of the sea and sustain U.S. regional influence. If allies and partners grow less willing or able to push back against China’s advances, that strategy will falter.

The contest in the South China Sea spans decades. Under the UN Convention on the Law of the Sea, a naturally formed area of land that remains above water at high tide is an island and is entitled to a territorial sea extending up to 12 nautical miles. If it can sustain human habitation or economic life of its own, it may also generate an exclusive economic zone extending up to 200 nautical miles; rocks that cannot do so may generate a territorial sea but not an exclusive economic zone. High-tide features can be subject to independent sovereignty claims even if they are located in another country’s maritime zones. But low-tide elevations—features only exposed at low tide—and fully submerged features lying beyond a territorial sea cannot be claimed as sovereign territory; if they lie within the exclusive economic zone or continental shelf of a coastal state, that state enjoys sovereign rights and jurisdiction over them. Brunei, China, Malaysia, the Philippines, Taiwan, and Vietnam each claim some or all of the features in the South China Sea. Together with Indonesia, these claimants also assert sovereign rights and jurisdiction in their exclusive economic zones, which overlap with China’s maritime claims. (Jakarta denies it has a dispute with China.) China, the United States, and other naval powers remain at odds over passage rights and freedoms of the seas.

Ten years ago, a tribunal in The Hague handed the Philippines a sweeping legal victory. Convened to hear a case the Philippines brought under the UN Convention on the Law of the Sea, the tribunal rejected any Chinese claim to historic rights within the “nine-dash line”—a U-shaped demarcation that encompasses much of the South China Sea but for which Beijing has never provided coordinates. It also clarified the maritime entitlements of the Spratly features, Scarborough Shoal (an atoll west of the Philippine main island of Luzon), and Reed Bank (a submerged atoll within the Philippines’ exclusive economic zone), finding that none of these features generates an exclusive economic zone. The high-tide features are at most entitled to a territorial sea. Reed Bank forms part of the Philippines’ exclusive economic zone and continental shelf.

Although legally binding only on the Philippines and China, the ruling strengthened the position of other Southeast Asian coastal states by affirming that neither China’s historic rights claim nor any exclusive economic zone extending from the features the tribunal examined could override their sovereign rights in their own exclusive economic zones. The tribunal did not decide on sovereignty over contested land........

© Foreign Affairs