China was an ancient civilization and her rule extended to many regions in history. Cantonese is referred to as Viet Yee same as Viet Nam meaning Viet South. That was because it was to the South of Guangzhou and the King of Annam was answerable to the King of Guangzhou who in term served at the pleasure of the Emperor of the Middle Kingdom.
Now you know why Vietnam formerly Annam claims in the SCS closely resembles those of China.
Although the West esp. the US alleged that China claimed the entire SCS, it is horseshit.
China only claimed those islands listed in her historical records. The facts are overwhelming and undisputable.
Even ICJ rejected Philippines claims due to lack of evidences. The Terra Nullius argument put forward by Phillipines were effectively overturned.
Due to many factors in China including civil wars, change of dynasties esp. climate change, many of these islands are now below sealevel.
Unfortunately many of these islands claimed by China happened to locate strategically in order for the Empire China to administer SCS effectively. That is why after 1945 many of these isles, shoals, etc were returned back to China and NOT Philippines, Vietnam, etc according to Cairo Declaration filed with UN.
These are also the opinions of many honest and renown historians.