The nine-dash line traces to a 1947 Republic of China map. China asserts 'historical rights' within the line — encompassing approximately 90% of the South China Sea — though never precisely defines what 'historical rights' means in legal terms.
The nine-dash line is one of the most consequential and contested cartographic claims in modern international relations.
How China Backs the Claim
China has progressively backed the with:
- Reclamation of Spratly Island features: turning small reefs and shoals into substantial artificial islands.
- Military installations: airstrips, hangars, radar systems, missile installations on the artificial islands.
- Coast guard enforcement: routine deployment of coast guard vessels in disputed waters.
- Maritime militia operations: paramilitary fishing fleets that assert Chinese presence and harass foreign fishermen.
- Naval exercises: regular People's Liberation Army Navy operations.
- Domestic legal claims: Chinese maritime law and administrative measures asserting jurisdiction.
- Diplomatic insistence: rejection of all foreign challenges to the claim.
The 2016 PCA Ruling
The July 2016 ruling in Philippines v. China unanimously found China's historical-rights claim within the nine-dash line was incompatible with UNCLOS — to which both countries are parties.
The ruling found:
- No historical-rights claim: China's historical rights claim has no legal basis under UNCLOS.
- No legal status for reefs: many features China occupies are reefs, not islands generating EEZs.
- Specific Chinese actions illegal: including harassment of Philippine fishermen and construction at Mischief Reef.
- No legal basis for Chinese interference with Philippine economic activities in the Philippines' EEZ.
China rejected the ruling and the proceedings. Beijing's position: the PCA had no jurisdiction; China had not consented to arbitration; the ruling is null and void. The Chinese position is legally untenable under UNCLOS arbitration provisions but is politically maintained.
A Tenth Dash?
A 'tenth dash' east of Taiwan appeared on a 2023 Chinese map causing diplomatic protest, suggesting potential of the claim. The : China may be expanding its maritime claims beyond the original nine-dash line to include waters around Taiwan.
Multidimensional Implications
The dispute affects:
- Fishing rights: Filipino, Vietnamese, Indonesian, and Malaysian fishermen face Chinese harassment in their traditional fishing grounds.
- Oil and gas exploration: contested areas contain potentially substantial hydrocarbon resources.
- : international shipping must navigate contested waters.
- The broader maritime order in Southeast Asia: the dispute tests whether UNCLOS-based maritime law can constrain great-power coercion.
- US-China relations: the South China Sea is one of the most active US-China strategic flashpoints.
- Regional alignment: ASEAN states' positions on the South China Sea shape their broader great-power alignment.
Why It Matters
The nine-dash line dispute is one of the most consequential maritime disputes in modern international relations. The outcome of the dispute will substantially shape:
- Whether UNCLOS-based maritime law can constrain great-power claims.
- The South China Sea's future as international waters vs. Chinese controlled space.
- US alliance commitments to Philippines, Japan, Taiwan, and other partners.
- ASEAN's centrality in regional governance.
Real-World Examples
The July 2016 PCA ruling was the most important international legal action on the dispute. The 2023 'tenth dash' map raised concerns about Chinese claim expansion. The ongoing Chinese coast guard pressure on the Philippines at Second Thomas Shoal illustrates how the nine-dash line claim translates to operational maritime pressure on Southeast Asian states.
Example
The 2016 PCA ruling that China's nine-dash line claims have 'no legal basis' under UNCLOS — issued unanimously by a 5-member tribunal — remains the most important legal pronouncement on the dispute despite Chinese rejection.