This dissertation investigates the emergence and evolution of United States' national interests in the Arctic region, as well as examines the factors that influence how the U.S. engages in cooperative endeavors in the region with other Arctic states. Though geographically located on the periphery of broader global politics, the region nevertheless is geopolitically situated at the convergence of three continents—North America, Asia, and Europe—in an area historically significant to, but often underappreciated by, the U.S. Government. Two research questions frame this study. The primary research question asks: How have U.S. national interests in the Arctic region evolved over time, and what factors help explain the evolution of U.S. engagement in the region? U.S. perceptions of the region's geopolitical significance gives rise to a subsidiary question: To what degree has the U.S viewed the Arctic region as a zone of competition or a zone of cooperation? Drawing on a range of archival sources, academic literature, historical and contemporary U.S. Government documents—including several declassified documents, as well as personal interviews of key Arctic experts, this study analyzes the development of U.S. interests in the Arctic over four distinct time periods, collectively spanning over a hundred years. These time periods are pre-World War I to the end of World War II (1906-1945); the first half of the four-decade-long Cold War (1945-1967); the second half of the Cold War (1968-1989); and the post-Cold War period (1990-2017). The study produces three major findings. First, U.S. overall interest in the Arctic region increased and decreased in conjunction with how the U.S. perceived the region's overall geopolitical significance. This waxing and waning of U.S. involvement in the polar north generally aligned with the U.S. viewing the Arctic as either a zone of insignificance, competition, or cooperation at different phases over the study's time period. The study's second major finding is that U.S. security interests in the Arctic singularly dominated and shaped America's overall set of national interests that emerged in the region, particularly since World War II. While constituting a number of issues, the most important U.S. security interest in the Arctic has been ensuring freedom of navigation in and through the Arctic. The region's overwhelming maritime composition, along with freedom of navigation's centrality to America's broader global power and interests, ensures the security-driven focus of America's overall Arctic national interests. The final key finding reveals that U.S. Arctic cooperative engagement is conditional. Geopolitical perceptions of the Arctic as either a zone of competition or a zone of cooperation conditions America's willingness to engage with other Arctic states in the region. Since the end of the Cold War and the ensuing period of circumpolar cooperation, U.S. participation in Arctic cooperative arrangements has been conditioned on how much it perceives such arrangements intrude on U.S. autonomy and freedom to act in and through the region. / Doctor of Philosophy / The Arctic is a vast and sparsely populated region that historically has been viewed geographically and geopolitically peripheral to the rest of the world. The United States has not always considered the region important, even though it has territory there. This study asks two questions. First: How have U.S. national interests in the Arctic region evolved over time, and what factors help explain the evolution of U.S. engagement in the region? Second: To what degree has the U.S viewed the Arctic region as a zone of competition or a zone of cooperation? Three major findings emerge from this study, which covers the early 20th century to the second decade of the 21st century—more than a hundred years. First, the evolution of U.S. interests in the Arctic region have waxed and waned in concert with how important the U.S. perceives the region. Second, America's security interests in the Arctic region dominate and drive its overall approach to the region. Finally, U.S.'s willingness to cooperatively engage with other Arctic states in the region depends on how the U.S. believes such engagements effect its ability to act in and through the Arctic region. The Arctic region is becoming more geopolitically important than at any time since at least the Cold War. Rapid global warming could potentially make the region's historically inaccessible shipping routes and vast natural resources accessible by 2050. With Russia already the largest Arctic presence, and China's increased focus on the Arctic, the region could become a space for strategic competition that could threaten U.S. national interests. This study provides the policy community the background and context to navigate the geopolitical challenges and opportunities being unleashed in the Arctic region.