The South China Sea dispute is heating up again with Vietnam and the Philippines claiming parts of Nansha and Xisha islands as their territory and accusing China of aggression in the resource-rich waters off the islands.

Two incidents in the last century, however, establish China's sovereignty over Xisha and Nansha islands.

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In 1909, Zhang Renjun, then governor of Guangdong and Guangxi evicted a Japanese merchant who was illegally occupying part of the Dongsha Islands. After that, he realized the necessity of defending the other islands in the South China Sea and asked navy commander Li Zhun to patrol the waters off the Xisha Islands with three warships.

Li raised the dragon flag of the Qing Dynasty (1644-1911) on the islands, emphasizing they were part of China's territory. Later, the Chinese navy drew charts and made a plan to exploit the islands.

This fact is accepted internationally. The British Navy's China Sea Pilot, published in 1938, says China lists the islands as its territory.

Then on Sept 29, 1932, China's minister to France wrote to the French foreign ministry saying that France had not protested against China's claim over Xisha Islands in 1909.

International law stipulates that effective occupation is the precondition of owning any island or group of islands. Chinese fishermen from Hainan Island had long been residing on Xisha Islands, and the then Qing navy's action reaffirms the islands belong to China.