Consider this a tale of two treaties.
A week that has seen the Philippines and the United States discuss spy flights over the South China Sea, and Japan name islets in the disputed Diaoyu Islands, highlights some intriguing wrinkles in the documents that tie the security of both countries to Washington.
When Tokyo takes action over the Diaoyus- which it calls the Senkaku Islands- it does so knowing it risks infuriating Beijing, but also with the knowledge that Washington has stated that the islands fall within the US-Japan mutual defence treaty.
Manila, however, faces a more ambiguous position from Washington over the claims in the South China Sea that it disputes with China and other regional countries.
Those differences help, in part, explain some of the swift moving military diplomacy now unfolding across the region.
Last weekend, Philippines Defence Minister Voltaire Gazmin emerged from discussions with US officials to talk up the need for an increased US military presence as a South China Sea deterrent, specifying possible rotations of US surveillance planes and new combat ships.