This book examines why Japan and South Korea have responded so differently to China’s rise, analysing how international pressures and domestic politics together shaped their strategic choices. Drawing on secondary literature, government documents, and interviews in Japan and South Korea, the book combines qualitative comparative case studies with process tracing to uncover the determinants of each state’s China policy. It shows that geography, material capabilities, and different stakes in the Korean Conflict produced more tensions with Japan, while incentivising cooperation for South Korea. Domestic factors – including political polarisation over China policy and the distribution of power between the chief executive and the bureaucracy – explained why South Korea’s approach fluctuated more than Japan’s across administrations. By advancing a neoclassical realist explanation that integrates both international and domestic variables, the author challenges arguments that rely solely on structural pressures, historical legacies, or US influence, and offers a more comprehensive account of how states navigate rising powers. This volume will be of interest to scholars, students, and practitioners working on international relations, East Asian politics, China’s rise, foreign policy analysis, decision-making processes, and comparative politics. It will also appeal to policymakers and analysts concerned with security dynamics in Northeast Asia.