While seeking closer economic relations with China, not least under the frame of the Belt and Road Initiative (BRI), the three Southeast Asian nations cooperate deeply with the United States in security matters. A major trigger for the latter collaboration is Beijing's assertive behaviour in the South China Sea. A key finding, based on a new hedging concept developed by the author, is that Vietnam applies the most robust and planned hedging strategy, while the Philippines reply more on an ad hoc basis to Chinese policies and actions.
You can find more details of Dr. Gerstl's book in the following link.