China Primer: South China Sea Disputes
link to page 1 
Updated August 21, 2023
China Primer: South China Sea Disputes
Overview
some of them. Vietnam occupies the most land features in
Multiple Asian governments assert sovereignty over rocks,
the island chain; Taiwan occupies the largest. In the eastern
reefs, and other geographic features in the heavily
part of the sea, China, Taiwan, and the Philippines claim
trafficked South China Sea (SCS), with the People’s
Scarborough Shoal; China has controlled it since 2012.
Republic of China (PRC or China) arguably making the
China’s “nine-dash line” and Taiwan’s similar “eleven-dash
most assertive claims. The United States makes no
line” overlap with the theoretical 200-nautical-mile (nm)
territorial claim in the SCS and takes no position on
EEZs that five Southeast Asian countries—Brunei,
sovereignty over any of the geographic features in the SCS,
Indonesia, Malaysia, the Philippines, and Vietnam—could
but U.S. officials have urged that disputes be settled
claim from their mainland coasts under the 1994 United
without coercion and on the basis of international law.
Nations Convention on the Law of the Sea (UNCLOS).
Separate from the sovereignty disputes, the governments of
the United States, China, and other countries disagree over
Figure 1. The South China Sea
what rights international law grants foreign militaries to fly,
sail, and operate in a country’s territorial sea or Exclusive
Economic Zone (EEZ). The last several Congresses have
examined China’s efforts to use coercion and intimidation
to increase its influence in the SCS and have passed
legislation aimed at improving the ability of the United
States and its partners to protect their interests, including
freedom of navigation and overflight.
The SCS is one of the world’s most heavily trafficked
waterways. An estimated $3.4 trillion in ship-borne
commerce transits the sea each year, including energy
supplies to U.S. treaty allies Japan and South Korea.
According to the U.S. Energy Information Administration,
the SCS contains about 11 billion barrels of oil rated as
“proved” or “probable” reserves—a level similar to the
amount of proved oil reserves in Mexico—and 190 trillion
cubic feet of natural gas. The SCS also contains significant
fish stocks, coral, and other undersea resources.
Ongoing Disputes
Source: CRS graphic.
Disputes over Sovereignty
Dispute over Freedom of the Seas
PRC officials assert “indisputable sovereignty over these
A dispute over how to interpret UNCLOS underlies U.S.-
islands [of the SCS] and their adjacent waters” without
China tensions over U.S. military operations in and over the
defining “adjacent waters.” The PRC government depicts
SCS and other waters off China’s coast. The United States
its claims with a “nine-dash line” (see Figure 1) that
and most other countries interpret UNCLOS as giving
encompasses approximately 62% of the SCS, according to
coastal states the right to regulate economic activities
the U.S. Department of State. (The estimate is based on the
within their EEZs, but not the right to regulate navigation
International Hydrographic Organization’s definition of the
and overflight through the EEZ, including by military ships
SCS’s geographic limits—a definition cited by the State
and aircraft. China, Vietnam, and some other countries hold
Department that includes waters well to the south and west
the minority view that UNCLOS allows them to regulate
of the nine-dash line, extending toward the southern part of
both economic activity and foreign militaries’ navigation
the Malay Peninsula.) The PRC has never explained
and overflight through their EEZs.
definitively what the dashed line signifies.
The U.S. Navy routinely operates in the SCS and the
In the northern part of the SCS, China, Taiwan, and
Taiwan Strait, including transits of the Taiwan Strait and
Vietnam contest sovereignty of the Paracel Islands; China
Freedom of Navigation Operations (FONOPs) near the
has occupied them since 1974. The PRC and Taiwan also
Spratly and Paracel islands to challenge maritime claims
claim Pratas Island, which Taiwan controls. In the southern
that the United States considers to be excessive. U.S. Air
part of the sea, China, Taiwan, and Vietnam each claim all
Force and Navy aircraft fly surveillance and reconnaissance
of the approximately 200 Spratly Islands, while Brunei,
missions in international airspace above the waters of the
Malaysia, and the Philippines, a U.S. treaty ally, claim
SCS, including airspace that is close to (but outside of)
China’s airspace. China regularly conducts military
https://crsreports.congress.gov
China Primer: South China Sea Disputes
activities in the SCS, and objects strenuously to U.S.
Renewed tensions could implicate the United States. In
military activities there. PRC officials often say that U.S.
2023, new Bilateral Defense Guidelines strengthened U.S.
military operations in the SCS undermine regional stability.
security commitments under the U.S.-Philippines Mutual
Defense Treaty, stating that armed third-party attacks
China and the other SCS claimants (except Taiwan, which
against Philippine armed forces, including coast guard,
is not a member of the U.N.) are parties to UNCLOS. The
aircraft, or public vessels “anywhere” in the SCS would
United States is not a party, but has long had a policy of
invoke U.S. mutual security commitments under the treaty.
abiding by UNCLOS provisions relating to territorial
waters, the EEZ, and navigational rights. UNCLOS allows
China’s Artificial Islands
state parties to claim 12-nm territorial seas and 200-nm
Between 2013 and 2015, China undertook extensive land
EEZs around their coastlines and “naturally formed” land
reclamation (i.e., island-building operations) in the SCS’
features that can “sustain human habitation.” Naturally
Spratly Island chain. According to DOD, the reclamation
formed land features that remain above water at high tide,
created around five square miles of artificial landmasses on
but which are not habitable, are entitled to 12-nm territorial
the seven disputed sites that China controls. China built
seas, but they are not entitled to 200-nm EEZs.
military infrastructure on and deployed advanced anti-ship
and anti-aircraft missile systems and other military
Flashpoints
equipment to the outposts. Although other claimants have
carried out reclamation and construction work at SCS sites
Dangerous Encounters at Sea
that they occupy, the scale of China’s reclamation work and
The U.S. and other governments have accused PRC military
militarization has greatly exceeded that of other claimants.
and non-military ships and aircraft of conducting unsafe
A 2022 DOD report on China’s military stated that these
maneuvers in and over the SCS that put other regional
outposts “allow China to maintain a more flexible and
actors at risk. The U.S. Department of Defense (DOD)
persistent military and paramilitary presence in the area,”
reported a “sharp increase in unsafe and unprofessional
which “improves China’s ability to detect and challenge
behavior” by PRC military ships and aircraft in 2021-2022.
activities by rival claimants or third parties and widens the
U.S. officials argue that some of these behaviors were
range of response options available to Beijing.”
“inconsistent with” bilateral and multilateral agreements
regarding air and maritime safety to which China is party.
Regional Cooperation
China and the 10-member Association of Southeast Asian
Tensions between China and Other Claimants
Nations (ASEAN) have been negotiating a code of conduct
For several decades, tensions in the South China Sea have
for parties in the SCS since 2002. Some observers say that a
periodically flared between China and other claimants (the
binding code is unlikely, and allege that China has
PRC and Vietnamese navies engaged in armed combat over
prolonged the negotiations to buy time to carry out actions
some of the islands in the 1970s and 1980s, for example).
aimed at further strengthening its position in the SCS.
In the past decade, tensions have been greatest between
The U.S. government seeks to enhance allies’ and partners’
China and the Philippines. In 2013—the year after China
maritime domain awareness in the South China Sea. In
gained de facto control of Scarborough Shoal following a
2022, the Quadrilateral Security Dialogue—a grouping of
confrontation between Chinese and Philippine ships—the
the United States, Japan, Australia, and India known as the
“Quad”—
Philippines sought arbitration under UNCLOS over PRC
announced an effort to improve maritime domain
actions in the SCS. In 2016, an UNCLOS arbitral tribunal
awareness throughout the Indo-Pacific, including the SCS.
ruled (among other things) that China’s nine-dash line
The U.S. Navy conducts patrols and exercises in the SCS
claim had “no legal basis” and that China violated the
with regional partners, including Australia, Canada, India,
Philippines’ sovereign rights by interfering with Philippine
Japan, and the Philippines.
vessels, damaging the maritime environment, and engaging
Select Legislation
in reclamation work on a feature in the Philippines’ EEZ.
Under a security assistance program currently known as the
The United States has urged China and the Philippines to
Indo-Pacific Maritime Security Initiative, authorized by
abide by the ruling, which under UNCLOS is binding on
Congress in the National Defense Authorization Act
both parties. China declared the ruling “null and void.”
(NDAA) for Fiscal Year (FY) 2016 (P.L. 114-92) and
modified in subsequent NDAAs, the United States has
In August 2023, China Coast Guard and maritime militia
sought to improve the ability of regional countries to
vessels fired a water cannon and took other actions to
enhance maritime domain awareness and patrol their EEZs.
obstruct a Philippine Coast Guard escort mission to
The NDAA for FY2021 (P.L. 116-283) established a
resupply a marine detachment stationed at a grounded
Pacific Deterrence Initiative (PDI) to strengthen U.S.
Philippine Navy vessel at Second Thomas Shoal, a
defense posture in the Indo-Pacific region, addressing
Philippine outpost in the Spratly Islands. PRC military and
issues such as those in the SCS. Congress extended and
coast guard vessels have conducted similar activities during
expanded the PDI in subsequent NDAAs. The House- and
resupply missions on several occasions since 2014. In
Senate-passed bill for an FY2024 NDAA (H.R. 2670)
February 2023, a PRC coast guard vessel targeted a
would further extend and expand the PDI.
Philippine coast guard vessel with a military-grade laser,
reportedly temporarily blinding some crew members.
Ben Dolven, Specialist in Asian Affairs
Caitlin Campbell, Analyst in Asian Affairs
Ronald O'Rourke, Specialist in Naval Affairs
https://crsreports.congress.gov
China Primer: South China Sea Disputes
IF10607
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF10607 · VERSION 11 · UPDATED
Updated August 21, 2023
China Primer: South China Sea Disputes
Overview
some of them. Vietnam occupies the most land features in
Multiple Asian governments assert sovereignty over rocks,
the island chain; Taiwan occupies the largest. In the eastern
reefs, and other geographic features in the heavily
part of the sea, China, Taiwan, and the Philippines claim
trafficked South China Sea (SCS), with the People’s
Scarborough Shoal; China has controlled it since 2012.
Republic of China (PRC or China) arguably making the
China’s “nine-dash line” and Taiwan’s similar “eleven-dash
most assertive claims. The United States makes no
line” overlap with the theoretical 200-nautical-mile (nm)
territorial claim in the SCS and takes no position on
EEZs that five Southeast Asian countries—Brunei,
sovereignty over any of the geographic features in the SCS,
Indonesia, Malaysia, the Philippines, and Vietnam—could
but U.S. officials have urged that disputes be settled
claim from their mainland coasts under the 1994 United
without coercion and on the basis of international law.
Nations Convention on the Law of the Sea (UNCLOS).
Separate from the sovereignty disputes, the governments of
the United States, China, and other countries disagree over
Figure 1. The South China Sea
what rights international law grants foreign militaries to fly,
sail, and operate in a country’s territorial sea or Exclusive
Economic Zone (EEZ). The last several Congresses have
examined China’s efforts to use coercion and intimidation
to increase its influence in the SCS and have passed
legislation aimed at improving the ability of the United
States and its partners to protect their interests, including
freedom of navigation and overflight.
The SCS is one of the world’s most heavily trafficked
waterways. An estimated $3.4 trillion in ship-borne
commerce transits the sea each year, including energy
supplies to U.S. treaty allies Japan and South Korea.
According to the U.S. Energy Information Administration,
the SCS contains about 11 billion barrels of oil rated as
“proved” or “probable” reserves—a level similar to the
amount of proved oil reserves in Mexico—and 190 trillion
cubic feet of natural gas. The SCS also contains significant
fish stocks, coral, and other undersea resources.
Ongoing Disputes
Source: CRS graphic.
Disputes over Sovereignty
Dispute over Freedom of the Seas
PRC officials assert “indisputable sovereignty over these
A dispute over how to interpret UNCLOS underlies U.S.-
islands [of the SCS] and their adjacent waters” without
China tensions over U.S. military operations in and over the
defining “adjacent waters.” The PRC government depicts
SCS and other waters off China’s coast. The United States
its claims with a “nine-dash line” (see Figure 1) that
and most other countries interpret UNCLOS as giving
encompasses approximately 62% of the SCS, according to
coastal states the right to regulate economic activities
the U.S. Department of State. (The estimate is based on the
within their EEZs, but not the right to regulate navigation
International Hydrographic Organization’s definition of the
and overflight through the EEZ, including by military ships
SCS’s geographic limits—a definition cited by the State
and aircraft. China, Vietnam, and some other countries hold
Department that includes waters well to the south and west
the minority view that UNCLOS allows them to regulate
of the nine-dash line, extending toward the southern part of
both economic activity and foreign militaries’ navigation
the Malay Peninsula.) The PRC has never explained
and overflight through their EEZs.
definitively what the dashed line signifies.
The U.S. Navy routinely operates in the SCS and the
In the northern part of the SCS, China, Taiwan, and
Taiwan Strait, including transits of the Taiwan Strait and
Vietnam contest sovereignty of the Paracel Islands; China
Freedom of Navigation Operations (FONOPs) near the
has occupied them since 1974. The PRC and Taiwan also
Spratly and Paracel islands to challenge maritime claims
claim Pratas Island, which Taiwan controls. In the southern
that the United States considers to be excessive. U.S. Air
part of the sea, China, Taiwan, and Vietnam each claim all
Force and Navy aircraft fly surveillance and reconnaissance
of the approximately 200 Spratly Islands, while Brunei,
missions in international airspace above the waters of the
Malaysia, and the Philippines, a U.S. treaty ally, claim
SCS, including airspace that is close to (but outside of)
China’s airspace. China regularly conducts military
https://crsreports.congress.gov
China Primer: South China Sea Disputes
activities in the SCS, and objects strenuously to U.S.
Renewed tensions could implicate the United States. In
military activities there. PRC officials often say that U.S.
2023, new Bilateral Defense Guidelines strengthened U.S.
military operations in the SCS undermine regional stability.
security commitments under the U.S.-Philippines Mutual
Defense Treaty, stating that armed third-party attacks
China and the other SCS claimants (except Taiwan, which
against Philippine armed forces, including coast guard,
is not a member of the U.N.) are parties to UNCLOS. The
aircraft, or public vessels “anywhere” in the SCS would
United States is not a party, but has long had a policy of
invoke U.S. mutual security commitments under the treaty.
abiding by UNCLOS provisions relating to territorial
waters, the EEZ, and navigational rights. UNCLOS allows
China’s Artificial Islands
state parties to claim 12-nm territorial seas and 200-nm
Between 2013 and 2015, China undertook extensive land
EEZs around their coastlines and “naturally formed” land
reclamation (i.e., island-building operations) in the SCS’
features that can “sustain human habitation.” Naturally
Spratly Island chain. According to DOD, the reclamation
formed land features that remain above water at high tide,
created around five square miles of artificial landmasses on
but which are not habitable, are entitled to 12-nm territorial
the seven disputed sites that China controls. China built
seas, but they are not entitled to 200-nm EEZs.
military infrastructure on and deployed advanced anti-ship
and anti-aircraft missile systems and other military
Flashpoints
equipment to the outposts. Although other claimants have
carried out reclamation and construction work at SCS sites
Dangerous Encounters at Sea
that they occupy, the scale of China’s reclamation work and
The U.S. and other governments have accused PRC military
militarization has greatly exceeded that of other claimants.
and non-military ships and aircraft of conducting unsafe
A 2022 DOD report on China’s military stated that these
maneuvers in and over the SCS that put other regional
outposts “allow China to maintain a more flexible and
actors at risk. The U.S. Department of Defense (DOD)
persistent military and paramilitary presence in the area,”
reported a “sharp increase in unsafe and unprofessional
which “improves China’s ability to detect and challenge
behavior” by PRC military ships and aircraft in 2021-2022.
activities by rival claimants or third parties and widens the
U.S. officials argue that some of these behaviors were
range of response options available to Beijing.”
“inconsistent with” bilateral and multilateral agreements
regarding air and maritime safety to which China is party.
Regional Cooperation
China and the 10-member Association of Southeast Asian
Tensions between China and Other Claimants
Nations (ASEAN) have been negotiating a code of conduct
For several decades, tensions in the South China Sea have
for parties in the SCS since 2002. Some observers say that a
periodically flared between China and other claimants (the
binding code is unlikely, and allege that China has
PRC and Vietnamese navies engaged in armed combat over
prolonged the negotiations to buy time to carry out actions
some of the islands in the 1970s and 1980s, for example).
aimed at further strengthening its position in the SCS.
In the past decade, tensions have been greatest between
The U.S. government seeks to enhance allies’ and partners’
China and the Philippines. In 2013—the year after China
maritime domain awareness in the South China Sea. In
gained de facto control of Scarborough Shoal following a
2022, the Quadrilateral Security Dialogue—a grouping of
confrontation between Chinese and Philippine ships—the
the United States, Japan, Australia, and India known as the
“Quad”—
Philippines sought arbitration under UNCLOS over PRC
announced an effort to improve maritime domain
actions in the SCS. In 2016, an UNCLOS arbitral tribunal
awareness throughout the Indo-Pacific, including the SCS.
ruled (among other things) that China’s nine-dash line
The U.S. Navy conducts patrols and exercises in the SCS
claim had “no legal basis” and that China violated the
with regional partners, including Australia, Canada, India,
Philippines’ sovereign rights by interfering with Philippine
Japan, and the Philippines.
vessels, damaging the maritime environment, and engaging
Select Legislation
in reclamation work on a feature in the Philippines’ EEZ.
Under a security assistance program currently known as the
The United States has urged China and the Philippines to
Indo-Pacific Maritime Security Initiative, authorized by
abide by the ruling, which under UNCLOS is binding on
Congress in the National Defense Authorization Act
both parties. China declared the ruling “null and void.”
(NDAA) for Fiscal Year (FY) 2016 (P.L. 114-92) and
modified in subsequent NDAAs, the United States has
In August 2023, China Coast Guard and maritime militia
sought to improve the ability of regional countries to
vessels fired a water cannon and took other actions to
enhance maritime domain awareness and patrol their EEZs.
obstruct a Philippine Coast Guard escort mission to
The NDAA for FY2021 (P.L. 116-283) established a
resupply a marine detachment stationed at a grounded
Pacific Deterrence Initiative (PDI) to strengthen U.S.
Philippine Navy vessel at Second Thomas Shoal, a
defense posture in the Indo-Pacific region, addressing
Philippine outpost in the Spratly Islands. PRC military and
issues such as those in the SCS. Congress extended and
coast guard vessels have conducted similar activities during
expanded the PDI in subsequent NDAAs. The House- and
resupply missions on several occasions since 2014. In
Senate-passed bill for an FY2024 NDAA (H.R. 2670)
February 2023, a PRC coast guard vessel targeted a
would further extend and expand the PDI.
Philippine coast guard vessel with a military-grade laser,
reportedly temporarily blinding some crew members.
Ben Dolven, Specialist in Asian Affairs
Caitlin Campbell, Analyst in Asian Affairs
Ronald O'Rourke, Specialist in Naval Affairs
https://crsreports.congress.gov
China Primer: South China Sea Disputes
IF10607
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF10607 · VERSION 11 · UPDATED