China is building artificial islands in the South China Sea to strengthen its military position, assert territorial control over disputed waters, and secure access to some of the world’s busiest shipping lanes. Since roughly 2013, China has transformed submerged reefs and rocky outcrops into full-scale islands equipped with airstrips, radar systems, and port facilities. The project serves multiple goals at once, but at its core, island building is about turning a contested waterway into something closer to Chinese-controlled territory.
Territorial Claims and the Nine-Dash Line
China claims sovereign control over nearly all of the South China Sea based on what it describes as 2,000 years of continuous, peaceful jurisdiction. That claim is represented by the “nine-dash line,” a boundary drawn on Chinese maps that sweeps in a massive U-shape across the sea, overlapping with the exclusive economic zones of Vietnam, the Philippines, Malaysia, Brunei, and Taiwan.
The problem for China is that international law, specifically the United Nations Convention on the Law of the Sea, doesn’t grant territorial rights based on historical use alone. In 2016, an international tribunal in The Hague ruled that the nine-dash line had no legal basis. China rejected the ruling entirely. Building islands is, in part, a way to create physical facts on the ground (or rather, on the water) that reinforce Chinese claims regardless of what international courts say. China treats these artificial islands as though they were naturally occurring landmasses and asserts that they carry traditional sovereign territorial rights, including control over surrounding waters.
Military Power Projection
The strategic military value of the islands is their primary purpose. Before construction, China’s navy and air force operated thousands of miles from these contested waters, with limited ability to project power into the southern stretches of the sea. The artificial islands solve that problem by functioning as permanent military outposts.
Key features on the largest islands, including Mischief Reef, Subi Reef, and Fiery Cross Reef in the Spratly chain, now include runways long enough for military aircraft, missile defense systems, radar installations, and deep-water harbors. These give China the ability to monitor and potentially restrict movement across a wide swath of ocean. In practical terms, the islands extend China’s military reach by hundreds of miles, creating a network of bases that would be extremely difficult for any rival to dislodge during a conflict.
Controlling a Global Trade Chokepoint
Roughly one-third of all global shipping passes through the South China Sea. Analysis from the Center for Strategic and International Studies estimated that about $3.4 trillion in trade moved through these waters in 2016 alone, representing around 21 percent of global trade. That makes it one of the most economically significant waterways on Earth.
For China specifically, the South China Sea is the gateway for energy imports from the Middle East and trade with Southeast Asia, Europe, and Africa. Controlling this corridor, or at least having the military infrastructure to influence traffic through it, gives China enormous leverage. In a crisis scenario, the ability to restrict or monitor passage through these waters would be a powerful bargaining chip against rival nations that depend on the same routes.
Oil, Gas, and Fishing Grounds
The South China Sea holds an estimated 3.6 billion barrels of oil and 40.3 trillion cubic feet of natural gas in proved and probable reserves, according to the U.S. Energy Information Administration. Much of this sits in uncontested areas near existing shorelines, but the Spratly Islands, where China has done the most building, may sit atop significant undiscovered deposits. The U.S. Geological Survey estimates the Spratly area holds a mean of 2.1 billion barrels of undiscovered oil and 8.0 trillion cubic feet of undiscovered natural gas.
Fishing is another major factor. The South China Sea has historically been one of the richest fishing grounds in the world, feeding hundreds of millions of people across Southeast Asia. But fish stocks have declined dramatically. Catch rates have dropped 66 to 75 percent over the past two decades, and coral reefs in the area are declining at roughly 16 percent per decade. In the Philippines, daily catches fell from about 20 kilograms per fisherman in 1970 to under 5 kilograms by 2016.
China has expanded its fishing fleet to roughly 200,000 vessels, many of which operate as a de facto maritime militia. Fishermen receive military training, government subsidies for fuel and equipment, and coast guard protection while operating in contested waters. These vessels serve a dual purpose: harvesting fish while physically occupying disputed territory. As one Chinese fisherman put it in a 2016 interview, “It is our water, but if we don’t fish there how will we claim it is our territory?” The presence of this massive fleet, backed by coast guard ships, pushes out smaller fishermen from neighboring countries who have legal rights to the same waters.
How the Islands Are Built
The construction process starts with dredging. Cutter suction and hopper dredgers scrape sand, coral rubble, and sediment from nearby seabeds and pump the slurry onto existing reefs and shallow formations. Bulldozers then level and compact the material, while concrete seawalls hold the structure together against waves and storms. The process can transform a submerged reef into a usable landmass of several hundred acres in a matter of months.
China carried out much of this work between 2013 and 2016 at an extraordinary pace, constructing over 3,200 acres of new land across multiple sites. The engineering is impressive but fragile. These are fundamentally piles of sand sitting on coral, reinforced with concrete. They require ongoing maintenance and remain vulnerable to typhoons and erosion.
Environmental Damage
The ecological cost has been severe. Marine biologist John McManus estimated that China’s activities, including dredging and giant-clam harvesting near the island sites, have caused roughly 55 square miles of damage to reef ecosystems on a timescale of decades. The direct footprint of island construction and harbor dredging accounts for about 6.5 square miles of reef destruction, but the broader disruption to surrounding ecosystems extends much further.
The South China Sea contains some of the most biodiverse coral reef systems on the planet. These reefs serve as nurseries for fish populations that the entire region depends on. Destroying them accelerates the decline in fish stocks that is already straining food security for millions of people across Southeast Asia. The irony is that by building islands partly to secure access to fishing grounds, China is degrading the very ecosystems that make those fishing grounds productive.
Why Other Countries Haven’t Stopped It
Several factors explain why the island building has continued largely unchecked. China began construction on reefs that were remote, submerged, and difficult to monitor. By the time satellite imagery revealed the scale of the work, many islands were already operational. Physically removing them would require a military confrontation that no country in the region, and no outside power including the United States, has been willing to initiate.
The 2016 tribunal ruling against China’s claims had no enforcement mechanism. International law in maritime disputes relies on voluntary compliance, and China simply refused to recognize the decision. Meanwhile, the economic relationships between China and its Southeast Asian neighbors make direct confrontation politically costly. Countries like the Philippines and Vietnam have protested through diplomatic channels and pursued legal avenues, but they lack the military capacity to challenge China’s navy directly. The United States conducts periodic “freedom of navigation” patrols through the area, sailing warships near the artificial islands to signal that it doesn’t recognize Chinese territorial claims, but these operations haven’t changed the situation on the ground.