From its creation in the early twentieth century, policymakers used the discourse of international law to legitimate Japan’s empire. Although the Japanese state aggrandizers’ reliance on this discourse did not create the imperial nation Japan would become, their fluent use of its terms inscribed Japan’s claims as legal practice within Japan and abroad. Focusing on Japan’s annexation of Korea in 1910, Alexis Dudden gives long-needed attention to the intellectual history of the empire and brings to light presumptions of the twentieth century’s so-called international system by describing its most powerful—and most often overlooked—member’s engagement with that system. Early chapters describe the global atmosphere that declared Japan the legal ruler of Korea and frame the significance of the discourse of early twentieth-century international law and how its terms became Japanese. Dudden then brings together these discussions in her analysis of how Meiji leaders embedded this discourse into legal precedent for Japan, particularly in its relations with Korea. Remaining chapters explore the limits of these ‘universal’ ideas and consider how the international arena measured Japan’s use of its terms. Dudden squares her examination of the legality of Japan’s imperialist designs by discussing the place of colonial policy studies in Japan at the time, demonstrating how this new discipline further created a common sense that Japan’s empire accorded to knowledgeable practice. This landmark study greatly enhances our understanding of the intellectual underpinnings of Japan’s imperial aspirations. In this carefully researched and cogently argued work, Dudden makes clear that, even before Japan annexed Korea, it had embarked on a legal and often legislating mission to make its colonization legitimate in the eyes of the world.