Abstract: As important concepts derived from alliance theory, minilateralism and quasi-alliance exhibit significant differences in practice. In the evolution of the trilateral cooperation mechanism between the United States, Japan, and the Philippines, although the U.S. portrays it as an exemplar of minilateralism under the “Indo-Pacific Strategy”, it demonstrates distinct “quasi-alliance” characteristics. Examining the seven dimensions of treaty constraints, exclusivity, scope of cooperation, cooperating parties, confrontational attributes, internal relationships, and cooperation goals, this paper argues that the United States, relying on its discourse hegemony, has framed this mechanism as “minilateralism”, while Japan and the Philippines have legitimized their policy of following the United States by joining it. Compared to “minilateralism”, the trilateral cooperation mechanism between the United States, Japan, and the Philippines is closer to a “quasi-alliance”, and is actually a “quasi-alliance” under the name of “minilateralism”. Its essence aims to strengthen strategic containment of China from security, economic, narrative, and other fields. The conceptual analysis of the trilateral cooperation mechanism between the United States, Japan, and the Philippines breaks through the narrative framework set by the United States at the theoretical level, providing a mirror for China to cope with the challenges brought by the trilateral cooperation mechanism between the United States, Japan, and the Philippines.

Key words: minilateralism, quasi-alliance, alliance theory, “Indo-Pacific Strategy”, the United States-Japan-Philippines