SITTING ATOP HIS HORSE named Tonto and donning a cowboy hat, Ryan Zinke clip-clopped his way to work in Washington, DC. The Montana native mustered all of the frontier swagger he could for his first day on the job as Secretary of the Interior, on March 1, 2017. Although Zinke’s stint in this post would last less than two years, he used his time to reshape the Interior Department into a pillar of Trump’s “Energy Dominance” doctrine. The plan was to make the United States, in Zinke’s words, “the strongest energy superpower this world has ever known.” Accordingly, he staffed the agency with industry insiders, drew up plans to open up nearly all federal waters to offshore drilling, and shrunk the Bears Ears National Monument — a site sacred to Native Americans, which was granted protections by the Obama administration — by more than a million acres.

To many observers, Zinke seemed like a strange choice for an agency tasked with the conservation of federal lands and management of the Grand Canyon and other national parks (surely, he was a far cry from Leslie Knope, the cheery but bumbling bureaucrat of Parks and Recreation). But a new book on the history of the Interior Department would suggest that Zinke — with his disregard for Native Americans, his intense desire to unlock underground resources, and his geopolitical understanding of the American “interior” — perfectly embodied the agency’s history.

Megan Black’s extraordinary book, The Global Interior: Mineral Frontiers and American Power, demonstrates the remarkable reach of the Interior Department. After moving settlers across the North American continent in the 19th century, Interior Department officials took their expertise abroad into American colonies and client states from 1898 onward. By the 1960s, the “interior” had expanded even beyond the bounds of American empire, stretching from the bottom of the ocean to the surface of the moon — a fitting jurisdiction for an agency nicknamed the “Department of Everything Else.”

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For the Interior Department, the boundary separating the interior from the exterior was blurry from the start. The agency was established in response to a series of foreign policy decisions that expanded American territory markedly in the 1840s — the same decade that gave us the glittery phrase “Manifest Destiny.” In those years, the country scooped up more than a million square miles of territory through annexation (of Texas), diplomacy (with Britain to acquire Oregon), and war (with Mexico). But expansion also led to difficult questions for a nation with a ramshackle federal government. Having grown by more than a third within a decade, how was Washington to manage its new lands, its new (mostly nonwhite) populations, and the chaotic rush of settlers westward?

The solution was the Interior Department. Founded by Congress in 1849, the Interior Department would make American rule real across these recently foreign landscapes. The fledgling department surveyed land expropriated from Native Americans and Mexicans, slapped on the label “public domain,” and then parceled it off for mostly white, small-plot farmers to settle and for businesses to purchase. It also absorbed the Bureau of Indian Affairs, the Patent Office, and, later, the Geological Survey — the resource-prospecting arm of the federal government, which would uncover the United States’s subterranean endowments. With the Interior Department’s so many seemingly disparate functions, John C. Calhoun bemoaned how the agency would encompass “everything upon the face of God’s earth.” But that turned out to be the right breadth for an agency that would soon be aiding an empire of global proportions, both within and beyond the continental United States.

Interior agents successfully carried out what Black calls the “spadework” of settler colonialism. They steamrolled over indigenous claims to sovereignty and settled hundreds of thousands of non-indigenous homesteaders by the turn of the 20th century. Even the new national parks played a colonizing role as they stripped Native Americans of land, facilitated tourism, and were patrolled by federal agents. The Lakota Sioux leader Black Elk rightly called these parks, such as Yellowstone, which was established in 1872, “little islands” of the federal government.

But the department’s “success” in promoting settler colonialism eventually began to trouble officials who worried that the country was running out of room to settle. The 1890 census — yet another task performed by the Interior Department — claimed that “the unsettled area had been so broken into” by settlers that there was scarcely “a frontier line” left. Some read this in existential terms. Frederick Jackson Turner went so far as to eulogize the frontier in American life. The Midwestern historian claimed that the “perennial rebirth” on the frontier had not only made the map of America, it also made Americans American — creating their “exuberance,” “individualism,” and sense of adaptation. And so, Turner gloomily asserted, “the closing of the frontier” marked the end of the “first period of American history.” It wasn’t clear what would follow.

While Turner’s argument gripped people’s imaginations — including officials in the Interior Department who were brooding over their own possible irrelevance — it didn’t fit with reality. Black argues that Turner’s “frontier thesis” proved incorrect because of, well, the Interior Department. In it, the American government had a bureaucracy — a “machinery of governance” — whose very task was to find and prepare “new frontiers.” The Interior Department had turned recently foreign land into American territory. Now, reaching the confines of the continent, the Interior Department would aid in the next period of American history — overseas colonialism.

At the end of the 1890s, the United States embarked on a new round of expansion, again by way of annexation (of Hawai’i), diplomacy (with Britain and Germany to take Samoa), and war (with Spain to take its colonies). And once again, the Interior Department’s colonial expertise in managing indigenous populations and reconnoitering landscapes came in handy. Borrowing from the Indian Service on the mainland, the Interior Department set up the Bureau of Non-Christian Tribes in the Philippines. The Interior Department also shipped out the Geological Survey, which was so busy mapping mineral resources that, according to one report, it did “not let much grass grow under its feet.” The “interior” was no longer continental. It now spread across the planet.

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But this isn’t a story about how the United States became just another member of the imperial club; after all, the American rise to global supremacy coincided with that club’s collapse. Black’s book sheds new light on this unusual fact of American and global history. She shows how, in the middle decades of the 20th century, the Interior Department’s machinery of governance helped the United States adapt its empire to a new world marked by self-determination and sovereign borders.

First, Washington rebranded its formal empire. In 1934, President Franklin Delano Roosevelt centralized imperial authority in a new agency, the Division of Territories and Island Possessions, and placed it under the Interior Department. Empire, in FDR’s vision, should be rational, perhaps even anti-imperial. Looking for someone to head the new agency who would fit such odd criteria, he reached out to Ernest Gruening, a progressive journalist who, only weeks before, had proclaimed the end of imperialism in a scathing New York Times article. Surprised by the invitation, Gruening told the president that “a democracy shouldn’t have any colonies.” Roosevelt replied with a smile and a shrug and acknowledged that Gruening might be right. Gruening accepted the post. But Black shows that placing an anti-imperialist at the helm of an empire was more imperial virtue signaling than it was imperial reform. For the Philippines, decolonization was delayed by a decade, and, for the rest of the United States’s colonies, independence never happened at all.

In addition to overseeing the formal empire, the Interior Department provided the United States with new tools to leap over sovereign borders and extend American influence abroad. Interior agents deployed their geological expertise by surveying lands, searching for resources, and preparing the way for American companies — all within foreign borders and typically at the invitation of those foreign states. It was seen as technical assistance or (as Black riffs on FDR’s Good Neighbor Policy) “the neighborly way to do extraction.”

This approach smashed the logic of holding colonial territory. Whereas empires had sought out colonies in order to secure resources, the Interior Department now granted American corporations access to mineral resources in sovereign states. Whether it was chrome in Afghanistan or oil in Sudan, the Interior Department located these resources and set up market means of attaining them, often serving as the middleman between American companies and foreign governments. This mechanism mattered a great deal for a country that faced an increasingly anti-imperial world while it was also anchoring the global economy in the midst of World War II and then the Cold War. An Interior report in 1949 stated that, despite only making up seven percent of the world’s population, the United States used half of the world’s minerals.

The Interior Department also found another creative way to expand its reach without crossing foreign borders. Black explains that, after much counsel from the Interior Department, President Harry Truman proclaimed the continental shelf — the parts of the American continent submerged under water — to be American territory. This was one of the largest land-grabs in American history, almost the size of the Louisiana Purchase, though it’s hardly remembered as such. The expansion shook international legal norms. Sovereignty used to extend three miles from a country’s shore — a vestige of how far an 18th-century cannon could fire — but now the Interior Department pushed it to 150 miles. And just like the old days of the western frontier, the Interior Department mapped and parceled off the continental shelf, though this time for offshore oil drilling.

Finally, the Interior Department developed strategies to access territories that couldn’t quite be colonized, such as the deep-sea floor at the bottom of international waters, which it declared to be a commons that any country could mine (or at least, any country with the requisite technology to plunge into waters 10,000 feet deep). In 1965, it even drew up plans to turn the Moon into a mining colony. If that sounds straight out of science fiction, then you might not be surprised to learn that Frank Herbert, the author of Dune, the novel published that same year, was friends with the Interior Secretary and had worked on the Continental Shelf Lands Act as a Senate staffer back in the 1950s. Cost and feasibility problems kept the lunar project from ever getting off the ground, but Black argues that it revealed the expansive ambition of American officials in a post-imperial age. Extraterrestrial colonialism, after all, had been only a distant dream of Cecil Rhodes, the British arch-imperialist who wistfully claimed: “I would annex the planets if I could.”

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By zooming in on the work of this important but too easily forgotten agency, The Global Interior deftly rearranges the last century and a half of American history in fresh and useful ways, which are informed, the author readily acknowledges, by the analysis in Mark David Spence’s Dispossessing the Wilderness: Indian Removal and the Making of the National Parks (1999), Genevieve Clutario’s dissertation, The Appearance of Filipina Nationalism: Body, Nation, Empire (2014), and other pioneering studies. Black reads the Spanish-American War alongside space satellites and places the American Indian Movement next to OPEC. Most notably, her book allows us to see how settler colonialism served as the staging ground for the United States’s rise to its superpower status. This isn’t a case of a historian imposing causation onto a faintly connected past. Black’s historical actors themselves were aware of the western frontier’s role. One Interior official announced in 1952 that the Global South had replaced the American West as the Interior Department’s raison d’être. And it was out west, he continued, that the Interior Department had acquired the “know-how” needed for the “opening of this new frontier,” a frontier that now spanned the world.

That Interior Department know-how can help decipher our odd lexicon of never-ending “final frontiers.” Five decades after Turner bemoaned the “closing of the frontier,” the Interior Department marketed Alaska as “our last frontier.” But this too would be superseded. The Interior Department helped American businesses reach into the “new frontier” of the Global South. Soon after, the Interior Department and NASA launched satellites into space, a domain the opening credits of a certain 1960s sci-fi television series named “the final frontier.” Given the Interior Department’s role in scrounging for foreign landscapes and preparing them for American influence, Black suggests, new frontiers have never been too far away.

The search for new frontiers continued during Zinke’s recent tenure as Secretary of the Interior, as he pushed offshore drilling to the outer edges of the continental shelf and turned wildlife refuges into extractable land. But Zinke’s free-wheeling ways of privatizing those frontiers was too much for the Interior Department to bear, and he was forced out at the beginning of this year. Zinke rode off into the sunset, taking a plush job in cryptocurrencies, a burgeoning industry that the United Nations recently designated a “new frontier.”

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Dexter Fergie is a PhD student of American and global history at Northwestern University, specializing in communications, infrastructure, and international relations.