Why the South China Sea Is So Contested

Stretching across roughly 3.5 million square kilometres, the South China Sea is one of the busiest and most strategically significant bodies of water on earth. It connects the Pacific and Indian Oceans, carries a significant share of global maritime trade, and sits atop substantial reserves of oil and natural gas. It is also the subject of overlapping territorial claims involving China, Vietnam, the Philippines, Malaysia, Brunei, and Taiwan.

The dispute has simmered for decades but has grown increasingly tense in recent years, drawing in the United States and other outside powers and raising concerns about the risk of military miscalculation.

Who Claims What?

China's claims are the most expansive. Beijing asserts sovereignty over the vast majority of the South China Sea based on what it calls historical rights, illustrated by the so-called "nine-dash line" — a demarcation that encompasses waters also claimed by several Southeast Asian nations.

In 2016, an international arbitration tribunal convened under the United Nations Convention on the Law of the Sea (UNCLOS) ruled that China's broad historical claims had no legal basis. China rejected the ruling and has continued to assert its position.

Other claimants include:

  • Vietnam — claims the Paracel and Spratly Islands, which have been a source of periodic confrontation.
  • The Philippines — claims parts of the Spratly Islands and has been increasingly assertive in pushing back against Chinese activity near its Exclusive Economic Zone (EEZ).
  • Malaysia and Brunei — have overlapping claims to portions of the Spratly Islands based on their continental shelf extensions.
  • Taiwan — maintains a claim nearly identical to China's, a legacy of both governments once claiming to represent all of China.

What Makes It Valuable?

Trade Routes

The South China Sea is one of the world's most important shipping lanes. Goods worth trillions of dollars pass through it annually, including energy supplies bound for Japan, South Korea, and China itself. Control over these waters — or the ability to disrupt passage — represents significant geopolitical leverage.

Natural Resources

The seabed is believed to contain substantial reserves of oil and natural gas, though estimates vary widely. Fishing grounds in the region are also vital food sources for hundreds of millions of people across Southeast Asia.

Military Positioning

Control of islands and reefs provides military basing opportunities. China has built and militarised artificial islands in the Spratlys, installing runways, radar systems, and weapons. This fundamentally changes the strategic balance of the region.

The Role of the United States

The U.S. does not make territorial claims in the South China Sea but conducts "freedom of navigation" operations to challenge what it regards as excessive maritime claims. Washington maintains mutual defence treaties with the Philippines, which creates the possibility that a clash involving Filipino vessels could draw the U.S. into a direct confrontation with China.

What to Watch For

  • Incidents between Chinese coast guard vessels and Philippine supply boats near contested reefs.
  • The pace of Chinese military infrastructure development on artificial islands.
  • Diplomatic efforts within ASEAN to develop a binding Code of Conduct for the region.
  • U.S.–China relations more broadly, which heavily influence the temperature of the dispute.

The South China Sea dispute is not simply a regional quarrel over rocks and reefs. It reflects broader questions about the international rules-based order, the limits of international law, and how rising powers assert themselves on the world stage. Staying informed about developments there is essential to understanding 21st-century geopolitics.