My word the southern reaches of the Chinese claim are extremely grabby! Is this just similar to haggling in a bazaar for an item listed at $30, which you personally value at $20 so you open with a lowballed offer of $10?
And while they fight amongst each-other, China voices support for one while undermining that support in another fashion. Pitting them against each-other is common.
Building the islands... well, everybody else who claims that area also seems to be building there. That could, arguably, be considered an act of war, but so far everybody's doing it and we do not yet have a war.