The Chinese need resources like water and raw materials for the next century. They will also need more food for a growing population. The fix is either land reclaimed from the sea or expansion for more farmland.. like how the Roman Empire expanded down south and used the North of Africa as their farms. So it may very well be that the rice growing countries of Vietnam, Laos, Thailand and Philippines are very feasible for long term expansion.
Does it want war? Probably not but it wouldn't mind flexing it's muscle like this is their part of the world and they can do what they want.. just like Russia in Ukraine.
Please. china's population growth is among the lowest & trending lower.
Three Gorges dam is among the engineering achievements of the ages, providing flood control, irrigation water & nearly 100 TWh of electricity. They have a lot of other ambitious plans, as well, like fracking for natural gas. Their total energy production is second only to the US.
Their current model of resource acquisition is value added trade, same as Japan. Their efforts at market penetration are enormous, worldwide.
They will, of course, attempt to utilize any resources they can successfully claim, starting with their own. The Spratlys are essentially low hanging fruit. None of their rivals can even begin to match the effort they'll put forth to do so. They don't need to start shooting to accomplish that, so they probably won't unless somebody like the Vietnamese are willing to sacrifice human lives in defiance. They can't win. The best that anybody but the Chinese can hope to get out of it is a small piece of the bounty through co-development agreement.
There's no way the US will stick their nose in it, and there's no way that the Chinese will provoke direct American involvement anywhere we have legit interests.
Might makes right? Ask TR. He took the isthmus, remember? Ask James K Polk, who took Texas, California & everything in between from Mexico.