Has anyone heard of Bach Long Vi island in the Gulf of Tonkin? It's equidistant between Hainan Island and Vietnam. I read on Wikipedia that China controlled it until 1887 when the French forced China to hand to their Indochina colony. China got the island back in 1945 from Japan, then the Communists took the island in 1955. Amazingly, China returned the island to Vietnam! Was it a gift? Why did Vietnam want or claim the island? The Wikipedia page appears to say it was in Chinese possession before 1887.
Handing over the island is another example of China making territorial concessions. You can't say China is expansionist if it's giving islands away.
Don't worry, ALL these islands are not going anywhere. China is rising very fast and has plenty of time to take back those islands under Chinese control when China is strong enough.
Everyone knows this, that's why they are so worried about China.
By 2030 even the US will be powerless to do anything to China in China's own backyard.
By 2030, China will be a full economic power (manufacturing, industry, trade, market, GDP, fiscal revenues), financial power, technological power and military power. With money, talent (engineers and scientists), know-how and technology, it will be near on impossible to fight China in the South China Sea and East China Sea.
Then all these islands will come under full Chinese control without firing a shot. Remember Sun Tzu?
This is pretty much the goal of the CPC, that's why economic development is the main priority for China right now. Because everyone knows time favours China. The more time goes by, the more things favour China due the gap between China and the developed world closing all the time and you add 1.3 billion people, and you get the picture.
Right now Paracel Islands (Xisha islands) are closer to China and are under Chinese control. Scarborough Shoal (Huangyan Island) is also under Chinese control. Now as Chinese capabilities increase, it can challenge the Diaoyu islands.
Spratly Islands (Nansha islands) are too far away right now. When the time is right, it will come under Chinese control too.
This is why many Chinese experts say we need 20 more years to reach full potential. Once China reaches its full potential, it's game over for everyone else. China is already very powerful right now but as powerful as it is now its nowhere near its full potential. Once China reaches full potential no one will be talking about island disputes.
This is why China is known to play the long game.