Contrary to the expectations that the US Cold War alliance system in the Asia- Pacific region would disintegrate with the disappearance of a communist threat as its raison d’etre, the basic structure of the US-led hub-and-spoke system in the region remains largely in place. Nonetheless, the circumstances informing the US Asia-Pacific alliances are no longer the same as during the Cold War years. Some US Asia-Pacific alliances have undergone significant transformations and morphed into more robust and comprehensive strategic partnerships, whereas others have failed to follow suit. Such divergence in alliance transformation in the Asia-Pacific has largely resulted from the capabilities gap' among US allies in responding to US requests for the expansion of alliance functions and development of cooperative ties among its allies and other partners. A comparative analysis of the ROK-US and US-Philippines alliances suggests that the capabilities gap between South Korea and the Philippines has been the main reason for the divergent paths of transformation that the two alliances have taken.