This essay is adapted from a new afterword to the paperback edition of The Line Becomes a River by Francisco Cantú, to be published by Riverhead in February.

In the summer of 2018, as the press began to cover stories of family separation following the implementation of the Trump administration’s “zero tolerance” immigration policy, Americans were forced to grapple with the human cost of border enforcement at a national level. Perhaps unsurprisingly, the greatest outcry came in response to photographs that distilled the policy’s cruelty into images of children crying at the feet of armed border guards and sleeping on bare floors inside cages—soon after their viral circulation, the president was forced to issue an executive order reversing the practice of separating families. That reversal, we have learned in recent months, was only partial, and has done little to address the underlying cruelty of our border enforcement practices—a point made newly clear just over a month ago when a group of Central American asylum seekers that included barefoot toddlers was met with tear gas at the San Diego/Tijuana border.

Because we are rightly habituated to believe in the innocence of children, because the “othering” of children requires a special degree of callousness, these images and stories have proved difficult to shake off—they have caused us to feel, in brief reverberating moments, a sense of horror at beholding our nation, our institutions, and perhaps even ourselves. But the separation of families and the teargassing of children do not represent isolated events in our history; we are merely seeing a chilling extension of the dehumanizing policies and rhetoric that were already in place.

I joined the Border Patrol more than a decade ago, and when I left in 2012 I had no intention of writing a book about my experiences there. As I settled into a new life, however, I began revisiting the journals I had kept during my years on the job as a way to make sense of where I had been, what I had seen, what I had done and not done, and they became the basis of my memoir, The Line Becomes a River. When I began writing, I knew that the book must be anchored by an exploration of the myriad ways violence becomes normalized along the border.

Living near the border means becoming conditioned to a degree of militarization and surveillance that would cause great alarm in any other part of the country. At immigration checkpoints between distant desert towns, automated cameras snap mugshots of you behind the wheel, and uniformed agents nod at drivers with light skin, waving them on to “have a nice day,” while requiring…