How do the American people benefit from protecting Vietnam and the Philippines? Not to sound trollish, but I genuinely do not see why spending billions in the region and antagonizing China really helps us.
From an idealistic standpoint, America supports the notions of state sovereignty and the U.N. Convention on the Law of the Sea simply out of principle. Like Apple’s stance on customer data privacy, the U.S. government defends freedom as a matter of pragmatism first, and then talks up the altruistic angle :)