Researchers, NGOs, and the Brazilin government have paid significant attention to the preservation of Brazil’s natural landscapes. As a result, more than 25 million ha have been added to the system of protected areas in the region. However, the size and legal status of many protected areas throughout the Brazilian Amazon are being eroded. Understanding the drivers and outcomes of these reductions to protected areas is essential for the long-term management and preservation of ecosystem services. The objective of this article is to understand the social, political, and institutional factors behind a 2012 reduction to Amazon National Park (ANP), the first one created in Brazil’s Amazonia. Regional, national, and international demands for cattle and gold spurred an influx of migrants to the region, which increased the demand for land in and around ANP. In addition, the park’s semi-circled boundary created confusion on the ground over its exact limits. Institutional conflicts among environmental and colonization federal agencies further compounded the problem. Lastly, national energy shortages motivated the federal government to seek a site for hydropower generation that overlapped park boundaries. The coalescence of these drivers resulted in the encroachment and eventual downsizing of ANP by 47,080 hectares, and in the modification of 43 percent of the pre-2012 perimeter of the park.