This dissertation examines the issue of societal change due to semi-peripheral action, and asks why it is that some societies managed to avoid colonization at the hand of the western powers during the colonial period. The issues at hand include the question of how to bound world-systems in order to determine when a society fully enters the modern world-system which Immanuel Wallerstein describes as a bounded entity that constitutes a social system based on capitalism. In addition, the issues include the question of core/periphery structure - that is the position of a given society in the modern world-system, and the question of agency that a given society is able to exercise when being incorporated into the modern world-system. This dissertation uses the empirical case studies of Japan and Tonga in order to propose an explanatory framework of semi-peripheral change that explains why some societies were colonized and others were not. This dissertation argues that each society was semi-peripheral at the point in which they were incorporated into the modern system, and because adaptability is a key feature of semi-peripheral action, these two societies were able to avoid colonization. This dissertation argues that societies that transform their dominant mode of production by creating a developmental state while also transforming their political systems in order to conform to Westphalian notions of the nation-state were able to adapt to the modern world-system, and were able to not only avoid colonization, but were able to set themselves on the path to eventual core status. Those societies that only opted for political change but did not transform their mode of production avoided colonization, but were relegated to the extreme periphery of the modern world-system. Societies that did neither were colonized and became peripheralized. This dissertation aims to be a contribution to world-systems theory that examines change in the world-system.