China Primer: South China Sea Disputes

Updated August 25, 2026

China Primer: South China Sea Disputes

Overview

Multiple Asian governments assert sovereignty over rocks,

reefs, and other geographic features in the heavily

trafficked South China Sea (SCS), with the People’s

Republic of China (PRC or China) arguably making the

most assertive claims. While United States makes no

territorial claim in the SCS and takes no position on

sovereignty over any of the geographic features in the SCS,

U.S. officials have long urged that disputes be settled

without coercion and on the basis of international law.

Separate from the sovereignty disputes, the governments of

the United States, China, and other countries disagree over

what rights international law grants foreign militaries to fly,

sail, and operate in a country’s territorial sea or exclusive

economic zone (EEZ). For more than a decade, some

Members have examined China’s efforts to use coercion

and intimidation to increase its control over the SCS and

have passed legislation aimed at improving the ability of

the United States and its partners to protect their interests.

also claim Pratas Island, which Taiwan controls. In the

southern part of the sea, the PRC, Taiwan, and Vietnam

each claim all of the approximately 200 Spratly Islands,

while Brunei, Malaysia, and the Philippines, a U.S. treaty

ally, claim some of them. Vietnam occupies the most land

features in the island chain; Taiwan occupies the largest. In

the eastern part of the sea, the PRC, Taiwan, and the

Philippines claim Scarborough Shoal; the PRC has

controlled it since 2012. The PRC’s and Taiwan’s maritime

claims overlap with the theoretical EEZs that five Southeast

Asian countries—Brunei, Indonesia, Malaysia, the

Philippines, and Vietnam—could claim under UNCLOS.

Figure 1. The South China Sea

An estimated one-fifth to one-third of global ship-borne

commerce transits the SCS each year, and U.S. allies and

partners like Japan, the Philippines, South Korea, and

Taiwan are dependent on its waterways for trade.

According to estimates cited by the U.S. Energy

Information Administration, the SCS contains “proved” or

“probable” reserves of approximately 3.6 billion barrels of

oil and 40.3 trillion cubic feet of natural gas. The SCS has

significant fish stocks, coral, and other undersea resources.

The PRC and the other SCS claimants (except Taiwan,

which is not a member of the United Nations) are parties to

the 1994 UN Convention on the Law of the Sea

(UNCLOS). The United States is not a party but has long

had a policy of abiding by UNCLOS provisions relating to

territorial waters, EEZs, and navigational rights. UNCLOS

allows state parties to claim 12-nautical mile (nm) territorial

seas and 200-nm EEZs around their coastlines and

“naturally formed” land features that can “sustain human

habitation.” Naturally formed land features that remain

above water at high tide, but which are not habitable, are

entitled to territorial seas, but they are not entitled to EEZs.

Disputes over Sovereignty

PRC officials assert “indisputable sovereignty over these

islands [of the SCS] and their adjacent waters” without

defining “adjacent waters.” The PRC government depicts

its claims with a “dashed line” (see Figure 1) that

encompasses approximately 62% of the SCS, according to

the U.S. Department of State. The PRC has never explained

definitively what the dashed line signifies.

In the northern part of the SCS, the PRC, Taiwan, and

Vietnam contest sovereignty of the Paracel Islands; the

PRC has occupied them since 1974. The PRC and Taiwan

Source: CRS. Boundaries from U.S. Department of State.

Dispute over Freedom of the Seas

A dispute over how to interpret UNCLOS underlies U.S.China tensions over U.S. military operations in and over the

SCS and other waters off China’s coast. The United States

and many other countries interpret UNCLOS as giving

coastal states the right to regulate economic activities

within their EEZs, but not the right to regulate navigation

and overflight through the EEZ, including by military ships

and aircraft. China, Vietnam, and some other countries hold

the view that UNCLOS allows them to regulate both

economic activity and foreign militaries’ navigation and

overflight in their EEZs.

The U.S. Navy routinely operates in the SCS and the

Taiwan Strait, including transits of the Taiwan Strait and

Freedom of Navigation operations (FONOPs) near the

Spratly and Paracel Islands to challenge maritime claims

that the United States considers to be excessive. U.S. Air

Force and Navy aircraft fly surveillance and reconnaissance

missions in international airspace above the waters of the

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China Primer: South China Sea Disputes

SCS, including airspace that is close to (but outside of)

China’s airspace. China regularly conducts military

activities in the SCS and objects to U.S. military activities

there. PRC officials argue that U.S. military operations in

the SCS undermine regional stability. Japan, Australia,

Canada, the United Kingdom, and India, among others, also

have operated naval vessels and aircraft in the SCS.

Flashpoints

Dangerous Encounters

The U.S. and other governments have accused PRC military

and non-military ships and aircraft of conducting unsafe

maneuvers in and over the SCS that put other regional

actors at risk. The 2025 U.S. Department of Defense (DOD,

which is “using a secondary Department of War

designation” under Executive Order 14347) report on

China’s military notes that in 2024 the PRC employed a

“range of increasingly aggressive tactics intended to assert

China's maritime claims while avoiding armed conflict,”

including “unsafe” and “unprofessional” maritime actions

and air intercepts.

Tensions Between China and the Philippines

For several decades, tensions in the South China Sea have

periodically flared between China and other claimants. (For

example, the PRC and Vietnamese navies engaged in armed

combat over some of the islands in the 1970s and 1980s.)

For more than a decade, tensions have been greatest

between China and the Philippines, which refers to the area

of the SCS within its EEZ as the West Philippine Sea. In

2013—the year after China gained de facto control of

Scarborough Shoal following a confrontation between PRC

and Philippine ships—the Philippines sought arbitration

under UNCLOS over PRC actions in the SCS. In 2016, an

UNCLOS arbitral tribunal ruled (among other things) that

China’s dashed line claim had “no legal basis;” that none of

the land features in the Spratly Islands are capable of

generating an EEZ; and that China violated the Philippines’

sovereign rights by interfering with Philippine vessels,

damaging the maritime environment, and engaging in

reclamation work on a feature in the Philippines’ EEZ. The

United States has urged China and the Philippines to abide

by the ruling, which under UNCLOS is binding on both

parties. China declared the ruling “null and void.”

The China Coast Guard and PRC maritime militia regularly

harass and block Philippine coast guard and fishing vessels

throughout the SCS, including at Scarborough Shoal and

Second Thomas Shoal, which houses a marine detachment

on a grounded Philippine Navy vessel, the BRP Sierra

Madre. After a series of incidents in which PRC vessels

prevented the resupply of the Philippine ship, in July 2024

the Philippines and China agreed to allow Philippine

vessels to deliver supplies to the marine detachment. In

September 2025, China declared a nature reserve at

Scarborough Shoal; both the United States and the

Philippines have rejected the declaration as unlawful. In

2026, the PRC has deployed a floating structure and buoys

in and around the Scarborough Shoal, despite protests from

the Philippine government.

Renewed tensions could have implications for the United

States. In 2023, the United States and the Philippines

announced Bilateral Defense Guidelines to strengthen their

Mutual Defense Treaty, stating that armed third-party

attacks against Philippine armed forces, including Coast

Guard, aircraft, or public vessels “anywhere” in the SCS

would invoke U.S. mutual security commitments under the

treaty. Trump Administration officials have reaffirmed the

“ironclad” U.S. commitment to the Philippines.

China’s Artificial Islands

Between 2013 and 2015, China undertook extensive land

reclamation (i.e., island-building operations) in the Spratly

Islands. According to DOD estimates, that reclamation

created around five square miles of artificial landmasses on

the seven disputed sites that China controls. China built

military infrastructure on and deployed advanced anti-ship

and anti-aircraft missile systems and other military

equipment to the outposts. The 2025 DOD report on

China’s military stated that these outposts “enable China to

maintain a more flexible and persistent military and

paramilitary presence in the area,” which “improves the

PRC’s ability to detect and challenge activities by rival

claimants or third parties and widens the range of response

options available to Beijing.” Since 2021, Vietnam has

accelerated reclamation work on SCS features it controls,

with its total area of artificial land estimated at 4.3 square

miles. Since 2025, the PRC has responded with its own

island building in the Paracel Islands.

Regional Cooperation

China and the Association of Southeast Asian Nations

(ASEAN) have been negotiating a code of conduct for

parties in the SCS since 2002. Observers say that a binding

code is unlikely and allege that China has prolonged the

negotiations to buy time to carry out actions aimed at

further strengthening its position in the SCS.

The U.S. government has sought to enhance allies’ and

partners’ maritime domain awareness in the SCS. In 2022,

the Quadrilateral Security Dialogue—a grouping of the

United States, Japan, Australia, and India—announced an

effort to improve maritime domain awareness in the IndoPacific, including the SCS. The U.S. Navy conducts patrols

and exercises in the SCS with regional partners, including

Australia, Canada, India, Japan, and the Philippines.

Select Legislation

Under a security assistance program currently known as the

Indo-Pacific Maritime Security Initiative, authorized by

Congress in the National Defense Authorization Act

(NDAA) for Fiscal Year (FY) 2016 (P.L. 114-92) and

modified in subsequent NDAAs, the United States has

sought to improve the ability of regional countries to

enhance maritime domain awareness and patrol their EEZs.

The NDAA for FY2021 (P.L. 116-283) established a

Pacific Deterrence Initiative (PDI) to strengthen U.S.

defense posture in the Indo-Pacific region and address

issues such as those in the SCS. Congress extended and

expanded the PDI in subsequent NDAAs, including the

FY2026 NDAA (P.L. 119-60).

Ben Dolven, Specialist in Asian Affairs

William Piekos, Analyst in Foreign Affairs

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China Primer: South China Sea Disputes

IF10607

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