I've been hearing a lot lately about the ASEAN conference and Chinese military aggressiveness in the South China sea.
China wants the undersea oil that happens to be in the territorial waters of Vietnam, Malaysia, Indonesia, and Philippines. A little thing like international law and sovereign territory don't seem to mean much to China (unless it's Chinese territory).
I expect when the US is out of the way, when the Chinese are seizing Taiwan they won't stop until all of the South China sea is under their control too.
What can the Philippines do except give in when there is no US to back them up? If there is anything of value down there, China will take it.
Mainland SE Asia has been pushing the chinee back for centuries.