This brief examines the historical dimension of the tensions between Japan and South Korea and its implications on the current breakdown in their bilateral relationship. It argues that the battle over historical memory has led to lasting animosity between the two countries, contributing to serious problems in their defence ties and creating space for China to expand its influence in the region. The brief explores why efforts to overcome the historical animosities have fallen short, underlines the threat posed by the tensions to the future of the US security alliance in the Pacific, and outlines the impacts on India’s strategy in the region.