Aerial Empire combines environmental and political history to argue that air shaped the United States’ colonization of the intermountain west. By focusing on environmental management and federal-Indian policy, it shows how claiming and regulating air as a natural resource both supported and subverted the nation’s control over the region in the twentieth century. A combination of white encroachment, warfare, diplomacy, and violence had transferred the region from Native to non-Native populations by the late nineteenth century. This process involved claiming western air, but appropriating the lower atmosphere required technology and policies devised during the twentieth century. Efforts to access and regulate air shaped twentieth-century U.S. expansion in New Mexico, Colorado, Montana, and Arizona, and turned a boundless atmosphere into a finite resource. Climate cures began the process of defining air as a natural resource, accelerated by aviation which compelled courts to legally distinguish navigable airspace from air rights in the 1920s. Nuclear science expanded atmospheric knowledge and smog undermined an approach to pollution based on dilution by 1950. As air pollution control shifted from a local to national issue, commercial and military jets increasingly crowded the skies. Environmental policy extended federal authority over air as a natural resource with the 1970 Clean Air Act, which tribes used to press federal recognition of their environmental sovereignty. Fluid and elusive, atmospheric motion subverted efforts to fix the sky in place and undermined territorial jurisdiction. Although modern legislation made air a material resource, the atmosphere remained interconnected with land in ways that complicated its regulation. Claiming air required seeing it as a material rather than an immaterial resource, and as a finite rather than infinite one. Tribes influenced and deployed environmental law to bolster Indigenous power and challenge the settler state’s authority over air, land, and Native peoples. Yet Indigenous and rural communities suffered disproportionate impacts of atmospheric transformations, such as nuclear testing, extractive industry, and military airspace. Efforts to claim, measure, map, and manage the atmosphere contributed to crucial changes in modern American society, including the transfer of Indigenous land, resources, and labor to settlers; the degradation and pollution of air with dangerous compounds and waste; the expansion of military control over new spaces; and the extension of federal authority through modern environmental policy. / 2028-10-31T00:00:00Z