The nine-dotted line, nine-dashed line, U-shaped line, nine-dash map and similar names, including (Chinese: 南海九段线; pinyin: nánhǎi jiǔduàn xiàn; literally: "Nine-segment line of the South China Sea"; Vietnamese: Đường lưỡi bò; literally: "cow's tongue line"), (and at various times also referred to by names such as "The 10 dashed line" and "The 11 dashed line"), refer to the demarcation line used initially by the government of the Republic of China (ROC / Taiwan), and subsequently also by the government of the People's Republic of China (PRC), for their claims of the major part of the South China Sea (SCS). The contested area in the SCS includes the Paracel Islands, the Spratly Islands, and various other areas including the Pratas Islands, the Macclesfield Bank and the Scarborough Shoal. The claim encompasses the area of Chinese land reclamation known as the "great wall of sand".
An early map showing a U-shaped eleven-dotted line was published in the then Republic of China on 1 December 1947. Two of the dots in the Gulf of Tonkin were later removed at the behest of Chinese Premier Zhou Enlai, reducing the total to nine. Subsequent editions added dashes to the other end of the line, extending it into the East China Sea.
Following the defeat of Japan at the end of World War II, the Republic of China re-claimed the entirety of the Paracels, Pratas and Spratly Islands after accepting the Japanese surrender of the islands based on the Cairo and Potsdam Declarations. In November 1946, the Republic of China sent naval ships to take control of these islands after the surrender of Japan.
The nine-dotted line was originally an eleven-dotted-line first shown on a map published by the Kuomintang government of the Republic of China (1912–1949) in December 1947 to justify its claims in the South China Sea. After the Communist Party of China took over mainland China and formed the People's Republic of China in 1949, the line was adopted and revised to nine as endorsed by Zhou Enlai. After evacuating to Taiwan, the Republic of China has continued its claims, and the nine-dotted line remains as the rationale for Taiwan's claims to the Spratly and Paracel Islands.
The nine-dotted line has been used by China to show the maximum extent of its claim without indicating how the dots would be joined if it was continuous and how that would affect the extent of the area claimed by China. The Philippines, Vietnam, Malaysia, Brunei and Indonesia have all officially protested over the use of such a line. Immediately after China submitted a map to the UN including the 9-dotted lines territorial claim in the South China Sea on May 7, 2009, the Philippines lodged a diplomatic protest against China for claiming the whole of South China Sea illegally. Vietnam and Malaysia filed their joint protest a day after China submitted its 9-dash line map to the UN. Indonesia also registered its protest, even though it did not have a claim on the South China Sea.
It is reported that in 2013 the PRC extended their claims with a new ten-dash map, but in fact the "new" dash is to the east of Taiwan, not in the South China Sea.
According to Philippine President Benigno Aquino III, "China’s 9-dash line territorial claim over the entire South China Sea is against international laws, particularly the United Nations Convention of the Laws of the Sea (UNCLOS)". Vietnam also rejected the 9-dotted line claim, citing that it is baseless and against the UNCLOS. In 2010, at a regional conference in Hanoi, Secretary of State Hillary Clinton announced that "The United States has a national interest in freedom of navigation, open access to Asia's maritime commons, and respect for international law in the South China Sea". The United States has also called for unfettered access to the area that China claims as its own, and accused Beijing of adopting an increasingly aggressive stance on the high seas.
However, as early as 1958, China released the official document The government statement on the territorial waters of the People's Republic of China, the statement stated that China's territorial waters width is twelve nautical miles and announced that this provision applies to "all the territory of People's Republic of China, including the Chinese mainland and offshore islands, Taiwan and its surrounding islands, the Penghu Islands, the Dongsha Islands, Xisha Islands, Zhongsha Islands, the Nansha Islands and other islands belonging to China. At this point, "nine-dotted line" on the South China Sea has been identified lawfully. In contrast, United Nations Convention of the Laws of the Sea (UNCLOS) , created in 1984, does not support claims based on sovereignty or title, instead,it only raise the right to continue using the waters for traditional purpose. 
While China has never used the 9-dotted line as an inviolable border to its sovereignty, this strategy together with the fact that China's authority has never officially explained the meaning of the 9-dotted line have led many researchers to try to derive the exact meanings of the 9-dotted line map in the Chinese strategy in the South China Sea. Some scholars believe that this line cannot be considered as a maritime boundary line because it violates maritime laws, , which states that a national boundary line must be a stable and defined one. The 9-dotted line is not stable because it has been reduced from 11 to 9 dashes in the Gulf of Tonkin as endorsed by Zhou Enlai without any reasons given. It is also not a defined line because it does not have any specific geographic coordinates and does not tell how it can be connected if it was a continuous line. In October 2008, the website WikiLeaks published a cable from the U.S. Embassy in Beijing reporting that Yin Wenqiang, a senior Chinese government maritime law expert, had "admitted" he was unaware of the historical basis for the nine dashes.
According to the Kyodo News, in March 2010 PRC officials told U.S. officials that they consider the South China Sea a "core interest" on par with Taiwan, Tibet and Xinjiang, but subsequently backed away from that assertion In July 2010 the Communist Party-controlled Global Times stated that "China will never waive its right to protect its core interest with military means" and a Ministry of Defense spokesman said that "China has indisputable sovereignty of the South Sea and China has sufficient historical and legal backing" to underpin its claims.
At the Conference on Maritime Study organized by the U.S.-based Center for Strategic and International Studies (CSIS) in June 2011, Su Hao of the China Foreign Affairs University in Beijing delivered a speech on China’s sovereignty and policy in the South China Sea, using history as the main argument. However, Termsak Chalermpalanupap, Assistant Director for Program Coordination and External Relations of the ASEAN Secretariat, said: “I don’t think that the 1982 United Nations Convention on the Law of the Sea (UNCLOS) recognizes history as the basis to make sovereignty claims”. Peter Dutton of the U.S. Naval War College agreed, saying, “The jurisdiction over waters does not have connection to history. It must observe the UNCLOS.” Dutton stressed that using history to explain sovereignty erodes the rules of the UNCLOS. It is understood that China ratified the UNCLOS in 1996.
Maritime researcher Carlyle Thayer, Emeritus Professor of Politics of the University of New South Wales, said that Chinese scholars using historical heritage to explain its claim of sovereignty shows the lack of legal foundation under the international law for the claim. Caitlyn Antrim, Executive Director, Rule of Law Committee for the Oceans of the USA, commented that "The U-shaped line has no ground under the international law because [the] historical basis is very weak". She added "I don’t understand what China claims for in that U-shaped line. If they claim sovereignty over islands inside that line, the question is whether they are able to prove their sovereignty over these islands. If China claimed sovereignty over these islands 500 years ago and then they did not perform their sovereignty, their claim of sovereignty becomes very weak. For uninhabited islands, they can only claim territorial seas, not exclusive economic zones (EEZ) from the islands”.
- Later revisions add claims to parts of the East China Sea.
- The Paracel Islands are occupied by the PRC, but are also claimed by Vietnam and the ROC.
- The Spratly Islands are disputed by the Philippines, PRC, ROC, Brunei, Malaysia, and Vietnam, who each claim either part or all the islands, which are believed (hoped) to sit on vast mineral resources, including oil and gas.
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