China's biggest economic problem is that its products are getting quite expensive. Not USA expensive, yet, but they are losing market share in some product categories to poorer countries like Vietnam, India, Bangladesh, the Philippines, and soon Myanmar. Consider the changes in Japan between 1950 and 1989 - China is most of the way through that same evolution.
The Chinese economy would die a quick death if they went to war against America and her allies over these islands/economic zone. They’d lose a war, plus lose Korea, Japan, Vietnam and the entire area as trading partners.
The history of SE Asia isn’t one of trust in China as a fair dealer. They fear a Chinese hegemony. China’s on the cusp of becoming an also-ran. You’ve got the equivalent of Cook County (Obama Country) trying to maintain control on a population that wants to be Hong Kong. They’re going to lose, but it can be smooth or bloody.