China has learned that and won't let borders in its vicinity being decided by Western powers anymore.
The reality is that no-one is going to take those islands away from China anymore as China understood the importance of physical occupation.
Those islands are thousands of miles from the US's mainland. Those exercises are geopolitical muscle flexing. Of course they are.
First, this isn't an island, it's a shoal. The only dry land to speak of is 2 skerrys (32 square feet of land in total). They are uninhabited.
Second, the shoal is 400 miles from mainland China. It's only about a 100 miles from the Philippines, who have a claim on the shoal.
Third, UN arbitration has sided with the Philippines. China rejected such arbitration, but of course they would, since they have no real claim here.
This isn't just "muscle flexing" it's the US helping out an ally, one that happens to be in the right.
The borders in the area where decided by Westerners, China was shortchanged and is now using the Western approach: Land, claim, defend.
The reality on the ground is that China (and that really does include both the PRC and Taiwan) claims this area and that it physically occupies it. Unless the Philippines and others propose to start a war the area is therefore de facto Chinese.
I found that one interesting. Reminded me of something.
https://www.google.co.uk/maps/@24.6285609,-82.8711957,2321m/...
Plus ça change...
There have been international conventions for many years on how sea control works. China does whatever it wants -- but that doesn't make the area Chinese, it means they're violating international agreements and conventions and treaties.