The evolving racial perceptions of the Japanese between 1735 and 1854 were shaped by both Western observers and emerging Japanese voices. Framed by Linnaeus's Systema Naturae and the forced opening of Japan's ports, this long century coincided with the global ascent of racial thought amid growing technological, commercial, and geopolitical disparities. While Western nations rapidly industrialized, expanded their empires, and formulated racial ideologies to justify their dominance, Japan remained a populous and militarily formidable nation - one poorly understood by Western cultures enthralled by the stirrings of "scientific" racism. This disconnect generated a unique tension in global racial discourse. In this definitive work, Rotem Kowner explores three central themes: the emergence of modern racial theory - defined by belief in immutable racial hierarchies - and its role in shaping Western views of the Japanese; the centrality of visual representation in constructing and reinforcing racial categories; and the concurrent development of a Japanese proto-racial discourse that often portrayed the Japanese as superior - directly opposing Western portrayals. This ideological clash would later fuel the racial conflicts of the twentieth century. Through a compelling analysis of textual and visual materials, A Hardening Hierarchy offers groundbreaking insights into the intertwined formation of Western and Japanese racial ideologies. Kowner establishes a vital historical link between early representations of the Japanese and the more virulent racial discourses that emerged in the modern era, providing an essential foundation for understanding racial conflict in East Asia.