Look at the included map, you see that "U" shaped line that encompassed entire Paracel and Spratly Island; this is the entire area known as South China Sea!
This entire large body of water belong to China since ancient time.
Also, Paracel Island were used to be at the hand of these Vietnamese until the PLA defeated them in a sea battle and reclaim it.
Now, Paracel Island have a very large air base and the fighters range can cover the entire South China Sea including the Spratly Island group.
