On Election Day, 2018, residents of Nogales, Arizona, began to notice a single row of coiled razor wire growing across the top of the city’s border wall. The barrier has been a stark feature of the town’s urban landscape for more than twenty years, rolling up and over hilltops as it cleaves the American town from its larger, Mexican counterpart. But, in the weeks and months that followed, additional coils were gradually installed along the length of the fence by active-duty troops sent to the border by President Trump, giving residents the sense that they were living inside an occupied city. By February, concertina wire covered the wall from top to bottom, and the Nogales City Council passed a unanimous resolution calling for its removal. Such wire has only one purpose, the resolution declared—to harm or to kill. It is something “only found in a war, prison, or battle setting.”

Living in Tucson, barely an hour north of the border, I have become familiar with both sides of Nogales, crossing over the border to shop, attend meetings, take gifts or supplies to deported friends, or volunteer at a soup kitchen for migrants. In December, as I walked through the pedestrian crossing, I passed by uniformed soldiers transporting long ladders to one side of the port of entry, but I barely registered their significance. The militarization of the borderlands has become so commonplace that one often grows numb to its manifestations. It can seem distant until it reaches out to touch you. Only months later, as I watched images of the concertina wire proliferating on my social-media feeds, did I finally understand what those ladders had been for.

In “The End of the Myth: From the Frontier to the Border Wall in the Mind of America” (Metropolitan), the historian Greg Grandin argues that America’s urge to wall off its borders marks the death of our most potent myth—the galvanizing vision of men and women seeking freedom along a vast frontier, a space for reinvention, unburdened by society, history, and one’s own past. Since the very inception of our country, he writes, the presence of a frontier has “allowed the United States to avoid a true reckoning with its social problems, such as economic inequality, racism, crime and punishment, and violence.” The ever-shifting and expanding frontier also acted as a physical barrier against invasion; as a national-security buffer against foreign enemies, Native Americans, and Mexicans; and as a tenuous escape valve for freed slaves, European migrants, and discontented laborers from crowded Eastern cities.

The frontier did not always have mythic connotations. In early America, the words “frontier,” “border,” and “boundary” held little emotional significance and were used interchangeably to describe the physical limits of the nation. America’s first dictionaries didn’t even include the word “frontier.” But as the U.S. government began to coördinate campaigns for the removal and the extermination of Native Americans, clearing the way for westward settlers, the meaning of “frontier” came to be pegged to the notion of civilizational struggle. By the dawn of the twentieth century, with Native Americans dwindling in number and largely relegated to reservations, the frontier had been fully transformed into something romantic and beckoning—an entire way of life. It became, Grandin writes, “a state of mind, a cultural zone, a sociological term of comparison, a type of society, an adjective, a noun, a national myth, a disciplining mechanism, an abstraction, and an aspiration.” For the dominant white culture, the word meant freedom.

The frontier also provided a new way of understanding American identity, history, and politics. At the end of the nineteenth century, the historian Frederick Jackson Turner announced his “frontier thesis”—the idea that, in his words, “the existence of an area of free land, its continuous recession, and the advance of American settlement westward explain American development.” American identity hinged upon its perpetual expansion. Our democracy, Turner wrote, “came out of the American forest and it gained strength each time it touched a new frontier.” Expansion was thus a fundamental good and an integral part of what set us apart from Europe—it was the very thing that made America great. But on the frontier, Grandin reminds us, settlers won greater freedom for themselves only by “putting down people of color, and then continuing to define their liberty in opposition to the people of color they put down.”

“The End of the Myth” aims, in part, to reposition race-based violence to the center of the frontier narrative, exposing it as foundational to today’s “border brutalism.” In this respect, Grandin’s study of the frontier serves as a vital corrective to popular conceptions, in the lineage of work by scholars like Richard White, Patricia Limerick, and Richard Slotkin. In a chapter on the Mexican-American War, for example, Grandin unflinchingly describes the savagery of U.S. troops during the conquest of the country’s continental neighbor. In one incident, more than a hundred Arkansas soldiers descended upon a group of Mexican war refugees in a cave, raping and slaughtering victims as they pleaded for mercy. Many of these rabid Army volunteers, Grandin notes, were former bounty hunters with an unchecked thirst for scalping their victims.

In passages like this, “The End of the Myth” is effectively in conversation with Cormac McCarthy’s seminal novel “Blood Meridian,” which follows a band of scalp hunters as they wreak carnage across the borderlands. Indeed, Grandin quotes from the novel, borrows its title for one of his chapters, and even draws on the cover art of the original, 1985 edition for his own book jacket—a closeup of one of Salvador Dali’s “phantom carts,” in which a horse-drawn wagon and its occupants become, upon further examination, indistinguishable from the expansive landscape and architecture that surround them. “Blood Meridian” is propelled by grisly, deeply researched depictions of the violence perpetrated by remorseless white American men, unconcerned with the traumas they were unleashing into history. Long celebrated as a disabused, revisionist “anti-Western,” McCarthy’s novel can also be understood as fuelling the illusion of frontier masculinity. Grandin, to his credit, rejects the temptation to dismiss the violence as being somehow typical of a particular time or place. The atrocities accompanying expansion are shocking now, and were shocking then: even war-hardened men like General Winfield Scott, the commander of U.S. forces during the Mexican-American War, found them heinous enough to “make Heaven weep, & every American, of Christian morals blush for his country.”

As settlement supplanted America’s physical frontier, a new project arose to extend Manifest Destiny beyond its former geographic limits. American imperialism provided the opportunity for “a new revolution,” Woodrow Wilson declared in 1901, a little more than a decade before ascending to the Presidency. During the Spanish-American War of 1898 and ensuing military campaigns in the Dominican Republic, Haiti, and Nicaragua, Americans had, in Wilson’s view, “made new frontiers for ourselves beyond the seas.” This form of expansion allowed a nation still recovering from the Civil War and Reconstruction to channel its aggression outward once more. Former Confederate soldiers were able to don the uniform of a newly unified country and earn patriotic recognition while still fighting to exert racial superiority over people of color. Letters sent home by soldiers enlisted in these campaigns, Grandin tells us, “are notably similar, lightheartedly narrating to family and friends how they would shoot ‘niggers,’ lynch ‘niggers,’ release ‘niggers’ into the swamp to die. . . .” Like those who had collected Native American scalps first as mercenaries and then as soldiers, these men learned that America’s new frontier was a place that could legitimatize a racist thirst for violence.