"Who will stand up to them?"

Probably no one, as long as the shipping lanes stay open. The Chinese always act out of a playbook that chases policy objectives that won't reach fruition for decades, maybe a hundred years. I don't think they are stupid enough to want a shooting war that would quickly sweep up everyone in the region.

They want something. They can get it through diplomacy, but diplomacy is not an option if no one is afraid of you. They have a gun in one hand, and the other is beckoning everyone to be reasonable.