This study explores the significance of the Taiwanese aboriginal territories that Japanese political and military leaders founded in the early 1870s. In April 1874, Meiji Japan dispatched expeditionary forces to the aboriginal territories on the basis of two cases of atrocities that the aboriginal people had committed against their “subjects” several years earlier and their claim that part of the island of Taiwan was terra nullius. By focusing on the discourse between the leaders during the years just before the expedition’s launch, this article argues that the first overseas military campaign was not motivated by a single issue on the part of the new imperial regime, but by a combination of several domestic and external concerns. These issues, which drove them into the expedition against the Taiwanese aborigines, were all linked by a single thread; namely, their concern with regard to national security. In this sense, from the Japanese perspective, the Japanese viewed the aboriginal territories as the stage upon which national survival could be secured in the late 19th century’s international environment, one in which the West enjoyed predominance.