My dissertation traces the role of Taiwanese who migrated to and settled in South China and Southeast Asia in developing a Japanese "southern imperial sphere." Between 1895 and 1945, the Taiwan Government-General and the Foreign Ministry sought to use the island and its inhabitants to spread political and economic influence among the Chinese diaspora who lived across the South China Sea littoral. Japanese officials and Taiwanese migrant-settlers fashioned Taiwanese, who shared linguistic, commercial, and social ties with the diaspora, as intermediaries between Chinese populations and Japanese institutions. Officials especially encouraged Taiwanese settlement in Xiamen, the nexus of the diaspora and, by the twentieth century, the most important treaty-port in South China, home to fourteen international powers and overlapping—and often competing—legal jurisdictions. By exploring the legal, ideological, and social mechanisms by which Taiwanese reproduced and challenged Japanese power, my project reevaluates the often ignored role of colonized subjects in building empire. Under the extraterritorial protection of the Japanese consulates, many Taiwanese settled beyond the treaty-ports among local Chinese, yet maintained strong ties with Taiwan, acting as "migrant-settlers." Taiwanese, Japanese, and Chinese made claims to shared ethnicity and history between them to encourage and justify Chinese inclusion in this imperial order, producing a form of "imperial citizenship" as the legal and cultural basis for the Japanese regime, and legitimating the Japanese Empire as a cooperative, Asian empire. As doctors, merchants, and lawyers, Taiwanese deployed kinship networks and Japanese knowledge to promote their businesses and justify expanding the empire through law. First in the port-cities of South China and Southeast Asia, and later in Japanese wartime military expansion, Taiwanese were crucial to building a regional Japanese southern imperial sphere.