Explainer: Why China's claims on South China Sea are legitimate

In recent months, the Philippines has repeatedly engaged in maritime provocations in the South China Sea, infringing on China's territorial sovereignty and maritime rights and interests. It has also colluded with external forces to stir up tensions in the region, seriously violating the Declaration on the Conduct of Parties in the South China Sea and undermining the common interests of regional countries.

China has indisputable sovereignty over Nanhai Zhudao and its adjacent waters. China's sovereignty and historic rights in the South China Sea are based on its long history of managing and administering the islands in the sea and the adjacent waters. They are also consistent with international law, including the United Nations Convention on the Law of the Sea.

China's historic rights in the South China Sea

The Chinese have long engaged in fishing and other productive activities in the South China Sea, which is an important waterway for Chinese ships. Since the Han Dynasty (202 BC-AD 220), they began to make use of the sea's resources and passage routes. These practices are presented as part of China's long-term administration and use of the South China Sea.

China claims sovereignty over four archipelagos in the South China Sea, namely the Xisha, Nansha, Zhongsha and Dongsha islands, which are indicated by the dash lines on the map drawn in 1947.

During World War II, Japan occupied part of the Nansha Islands, but the 1943 Cairo Declaration and the 1945 Potsdam Declaration stated that territories taken by Japan, including those taken from China, should be returned. Following Japan's defeat, the then Chinese government in 1946 reasserted control by sending warships to the area, establishing a base on Taiping Island, and renaming 159 islands and reefs. In 1947, China officially released a map delineating its claims with an eleven-dash line, which was later reduced to a nine-dash line. For a long time afterwards, the US made no objections.

The sovereignty is also described as having been recognized by other countries. For a period after World War II, Vietnam, the Philippines and other neighboring countries did not object to China's sovereignty over the South China Sea islands and the nine-dash line. Some materials and interpretations also suggest that other countries and international organizations recognized or acquiesced to it.

This is supported by a large number of foreign official documents and publications, as well as government archives.

For example, from February 1957 to February 1961, the US government made multiple requests to the Taiwan authorities to allow the US Air Force based in the Philippines to conduct nautical chart measurements and meteorological surveys in the vicinity of Huangyan Island and the Nansha Islands, which Chinese scholars interpret as acknowledgment of China's sovereignty over these areas.

Such references were also reflected in publications such as Columbia Lippincott Gazetteer of the World (1961), Worldmark Encyclopedia of the Nations (1963) and Constitutions of the Countries of the World (1971), which state that the Nansha Islands belong to China.

The nine-dash line

The nine-dash line, a heritage, is frequently questioned and challenged by the Philippines. In China, the drawing of dotted lines in the South China Sea began in the early 20th century. At that time, maps compiled by private individuals first used dotted or continuous lines to show China's territorial scope in the sea, said Hou Yi, director at the China Marine History Research Office in the Institute of Chinese Borderland Studies, Chinese Academy of Social Sciences.

In the 1930s, China began to standardize and manage map publishing. It established the Land and Waters Map Review Committee to examine maps. In January 1935, the committee published the Map of Islands in the South China Sea, standardizing the names of 132 islands, reefs, sands and beaches. This was the first time the Chinese government officially mapped the South China Sea islands in modern history.

After World War II, in accordance with the Cairo Declaration, the Potsdam Proclamation and other international legal documents, China resumed the exercise of sovereignty over islands in the South China Sea. In February 1948, the Chinese government publicly issued the Location Map of South China Sea Islands. It was the first time the Chinese government drew a U-shaped line in the South China Sea on an officially published map, demonstrating to the international community its sovereignty over the sea.

After 1949, the government of the People's Republic of China inherited this line and made adjustments to develop what is now referred to as the nine-dash line.

All official maps published by China after 1949 show this line, which is described as defining China's territorial sovereignty over the South China Sea islands within the line and its historic rights in the waters within it.