This book investigates the hypothesis that increases in U.S. military responsibilities in geographic regions (with limited resources)-or geo-environmental changes-lead to an increase in operational risk. It does so by analyzing two historical and one contemporary case study. The two historical case studies examine increases in U.S. military responsibilities in regions dominated by oceans, seas, and littoral regions-specifically, the Asia-Pacific region after the United States acquired the Philippines from Spain in 1898, and the Indian Ocean region in the 1950s to the 1980s after the United Kingdom began retrenching. The lessons and understanding gained from these cases studies is then applied to a case study examining the Arctic today. The book analyzes these increases in U.S. military responsibility through five variables: Doctrine, Organization, Technology, Threat, and Facilities, to determine their overall effect on operational risk. The conclusion is that the facilities variable is the most important to consider in addressing operational risk incurred through geo-environmental change.