The strategic rivalry between the United States and China has emerged in recent decades as the central axis of geopolitical developments in the Indo-Pacific region. Within this framework, the Quad Alliance has taken shape—and been revitalized—as an emerging security arrangement among four democratic powers (the United States, Japan, India, and Australia) with the aim of containing China’s growing influence and preserving regional balance. The central question of this article is: what factors have contributed to the redefinition of threat perception toward China that led to the revival of the Quad? Drawing on Stephen Walt’s Balance of Threat theory, the article rests on the assumption that the members’ shared perception of China as a threat—across four dimensions: aggregate power, geographic proximity, offensive capabilities, and offensive intentions—has been the main driver of their strategic convergence. The research method is qualitative and descriptive-analytical, and data have been collected through documentary analysis of official security and defense sources of Quad members, including national strategies, defense white papers, and statistical data. The findings indicate that the Quad Alliance is less a reaction to China’s power per se and more a response to a multi-layered perception of threat posed by China, which has fostered the emergence of an informal security cooperation framework in the Indo-Pacific region.