My dissertation examines the expansion of the Colombian nation-state and the penetration of a private property regime in Putumayo between 1893 and 1977. Located in the northwestern corner of the Colombian portion of the Amazon rainforest, the Putumayo is mostly recognized for being at the center of the operations of the infamous Anglo-Peruvian rubber company Casa Arana and for attracting major colonization as the coca economy expanded in the Amazon. However, the transformation of Putumayo between the end of the rubber boom and the beginning of the coca economy has received scarce scholarly attention. My dissertation addresses this gap by focusing on the three cycles of roadbuilding projects and colonization initiatives that transformed the Putumayo in the twentieth century. First, I reconstruct the history of the Capuchin Mission in Putumayo between 1893 and 1932. Motivated by the spiritual and material “civilization” of the Putumayo indigenous population, the missionaries led the construction of roads and the foundation of new settlements in the region for incoming nonindigenous Colombian settlers. Secondly, I examine the history of the Colombia-Peru war starting in 1932 and the later definition of the Colombian national borders in the Amazon rainforest during the 1930s. Facing an international threat to Colombian territory in the Amazon by Peruvian rubber barons, the national government started the construction of the roads that would allow the Colombian government to exercise national sovereignty in the region and populate it with Colombian citizens. Lastly, I explore the history of Putumayo’s oil industry developed and managed by U.S. company Texaco between 1942 and 1977. When oil exploration and exploitation began in Putumayo, the lack of a sufficient local labor force to engage in the construction of roads and pipelines to transport oil from Texaco-owned wells in the Amazon encouraged yet one more cycle of colonization in Putumayo.