Shortly after the Meiji government assumed administrative responsibilities in 1868, the Iwakura Mission left Japan to circumvent the globe, searching for information on institutions that could centralize a divided archipelago. In so doing, it encountered a world embarking on a new phase of imperial expansion. While the majority of the Mission's participants returned with visions of a large, expansion-oriented Japan, others saw their country's future as a small, neutral state. Debates over the suitability of either vision continued throughout the Taisho period, especially as Japan incorporated territories at its peripheries, including Ezo (Hokkaidō), the Ryūkyū Islands (Okinawa), Taiwan, and Korea. This paper examines the impact of the Mission participants' perspectives, which were informed by their first- and second-hand experience of American and European amalgamation of peoples of diverse cultural, ethnic, and racial origins. How did the participants' experiences influence their views on Japan's future as an expansionist state? What did their experiences teach them about the assimilation of peoples of diverse backgrounds? This paper identifies the legacy of these debates as extending to the present, where Japan seeks to rescind postwar restrictions against extending military powers beyond its borders.