From the founding of the American republic through the 19th century, the nation’s environmental policy mostly centered on promoting American settlers’ conquest of the frontier. Early federal interventions, whether railroad and canal subsidies or land grant acts, led to rapid transformations of the natural environment that inspired a conservation movement by the end of the 19th century. Led by activists and policymakers, this movement sought to protect America’s resources now jeopardized by expansive industrial infrastructure. During the Gilded Age, the federal government established the world’s first national parks, and in the Progressive Era, politicians such as President Theodore Roosevelt called for the federal government to play a central role in ensuring the efficient utilization of the nation’s ecological bounty. By the early 1900s, conservationists established new government agencies, such as the U.S. Forest Service and the Bureau of Reclamation, to regulate the consumption of trees, water, and other valuable natural assets. Wise-use was the watchword of the day, with environmental managers in DC’s bureaucracy focused mainly on protecting the economic value latent in America’s ecosystems. However, other groups, such as the Wilderness Society, proved successful at redirecting policy prescriptions toward preserving beautiful and wild spaces, not just conserving resources central to capitalist enterprise. In the 1960s and 1970s, suburban and urban environmental activists attracted federal regulators’ attention to contaminated soil and water under their feet. The era of ecology had arrived, and the federal government now had broad powers through the Environmental Protection Agency (EPA) to manage ecosystems that stretched across the continent. But from the 1980s to the 2010s, the federal government’s authority to regulate the environment waxed and waned as economic crises, often exacerbated by oil shortages, brought environmental agencies under fire. The Rooseveltian logic of the Progressive Era, which said that America’s economic growth depended on federal oversight of the environment, came under assault from neoliberal disciples of Ronald Reagan, who argued that environmental regulations were in fact the root cause of economic stagnation in America, not a powerful prescription against it. What the country needed, according to the reformers of the New Right, was unregulated expansion into new frontiers. By the 2010s, the contours of these new frontiers were clear: deep-water oil drilling, Bakken shale exploration, and tar-sand excavation in Alberta, Canada. In many ways, the frontier conquest doctrine of colonial Americans found new life in deregulatory U.S. environmental policy pitched by conservatives in the wake of the Reagan Revolution. Never wholly dominant, this ethos carried on into the era of Donald Trump’s presidency.