This book introduces an innovative model for studying the role of small states in building international organizations. The model categorizes these states into region-engaging, region-constraining, and region-adapting actors, depending on their particular type of involvement in regional politics. Ecuador and Uruguay are studied in depth and categorized as region-engaging small states in the context of building UNASUR, the South American Union of Nations. The book argues that these two nations show elements of a shared and collective identity that influence their region-engaging character. The author considers various factors such as governments driven by left-oriented ideology, the failure of economic integration projects, the overpowering influence of external agents, and the need for national and regional peace. These circumstances as well as the prospect of small states playing a leading role and ushering in a new type of political cooperation within UNASUR prompted Ecuador and Uruguay to support the building and consolidation of this alliance.