“The border’s like our back door,” a concrete salesman named Chris told me in January 2017. “You leave it open, and anyone can walk right in.” It was the day of Trump’s presidential inauguration, and we were chatting on the exhibition floor of a trade show in Las Vegas, called World of Concrete. Circular saws, cement mixers, gleaming new trucks – it was an unusual place to talk about the politics of immigration.

But the simple promise of a concrete wall between the US and Mexico had flung a business tycoon into the White House, and I wanted to understand what this was about.

Chris was a millennial from a small town in western Ohio. With a trim beard and short, sandy hair, he projected an air of casual self-sufficiency. “I don’t really like neighbors,” he quipped, speaking with a dose of wry humor about how far he chose to live from other people.

I was struck by the mismatch between the salesman’s genial manner and his suspiciousness, his sense of anyone beyond his home or country as a potential threat. I wondered, as we talked amid a sea of construction equipment, what it would take to build genuine warmth and concern for outsiders, rather than such walls.

For the last five years, I’ve crisscrossed the United States as an anthropologist, pursuing conversation and debate between the coasts and heartland. I set out in 2016 to grasp the appeal of the border wall, the fantasy of sealing off the country with a stark, symbolic barrier. What I learned is that such barricades appeal to many Americans because they resonate with familiar boundaries in their daily lives.

While Trump’s presidency has passed, the defensive thinking that drove his ascent remains a pervasive and powerful force. I think of the Gen Xer with a bushy beard and colorful tattoos down the length of his arms, whom I saw hawking a motion sensor lighting system with these words of advice: “I know it sounds cold, but you want to keep people away as best you can.” Or this motto and promise from the home security company ADT: “a line in the sand between your family and an uncertain world.” Time and again, I’ve heard such ideas expressed by Americans I’ve met and spoken with around the country in my job as an anthropologist: businessmen and truck drivers, police officers and media personalities.

The give and take of neighbors has long been a foundation for our democracy, philosopher Nancy Rosenblum writes. But cultural and economic forces have worked stark distinctions – insider v outsider, familiar v stranger, safety v threat – deep into the texture of our daily lives. These hard lines and everyday divides fuel our political troubles in ways we don’t always realize.

To get to this gated community on Florida’s Treasure Coast, you have to drive through a continuous stretch of walled compounds, everything inside hidden from view by towering hedges and palms. I show my credentials at the guardhouse, and the railway gate swings open. As I drive with the security director past sprawling homes and unnervingly empty streets, Timothy tells me about a residential population – wealthy, mostly white – primed for disaster and desperate for repose.

One out of every six American houses in a residential community is secured now by such community walls or fences, and I met Timothy to try to understand why.

Residents who live here are mostly seeking psychological assurance, he admitted: “They like us smiling and waving at them.”

Contemporary gated communities build on a century of intentional segregation and suburban white flight. Suburban interiors were designed as “escape capsules to enable their independence from the outside world”, architectural historian Andrea Vesentini has shown, built as shelters from the unpredictability of urban life. The pandemic has magnified the appeal of such distance and defense, with more features like security cameras, video doorbells and HEPA air filters built into new houses than ever before.

These histories have profoundly reshaped how Americans live in relation to each other, as much as where. So much of everyday life and leisure now takes place in secluded spaces. The front porch sessions with neighbors and passersby that once epitomized American social life have given way to more private gatherings on the backyard deck, or time with the television and other screens indoors. These changes lessen the chance for happenstance conversation with neighbors and strangers.

A realtor in Fargo, North Dakota, helped me understand the significance of these shifts. A fit man in his early 60s, Paul had worked in the Fargo-Moorhead metropolitan real estate market for more than 20 years. He took me one morning to a compact new house in a middle-class subdivision, the smell of fresh paint lingering in the cool air inside.

Standing in the living room and looking to the front, I felt enclosed in the space, almost hemmed in: the house was fronted by a three-stall garage and one narrow window on to the street and sidewalk. Turn to the back though, and you were flooded with light from every direction, the rear of the house framed with big panes of glass instead of walls.

“Doesn’t it bother people that there aren’t many windows in the front?” I asked Paul. “You can hardly see what’s happening on the street.”

“The inside is what they care about,” he replied. “And,” he added, pointing out the sunroom at the rear of the house and the back patio beyond, “living on the back. This is where we engage socially with our neighbors.”

The small patio was lodged between other private decks and yards, a place to socialize with others by choice rather than necessity. “This is my space, I’ll engage with who I want, when I want,” the realtor explained. “It’s a bit selfish,” he acknowledged.

Whether it comes to the climate emergency or systemic racism, the migrant crisis or the ongoing pandemic, so much turns on whether we can acknowledge and accept the intertwining of our separate lives. But it’s not just our homes that are styled now like defensive fortresses.

Over the last decade, imposing vehicles like SUVs and trucks have come to dominate the American car market, far outpacing smaller sedans in sales. These are automobiles designed with aggressive profiles and built as defensive steel cocoons, often marketed as ways to survive an uncertain and even hostile world. As an automotive designer in Los Angeles told me, such vehicles appeal in a society that is “suffering a case of insecurity”.

There is a political side to such choices: researchers have found that cities with more sedans than pickup trucks will probably vote Democratic in a presidential election, while those with more pickup trucks will probably vote Republican. But it isn’t simply a matter of signaling partisan affiliation through automotive choice. Vehicles say a lot about what people care most about.

Consider an exchange I had one morning in Los Angeles with the driver of a Cadillac Escalade, a few years ago. He was an Asian American dad, like me, and we’d run into each other on the driveway of a cheery and progressive nursery school on the Westside. I’d walked my daughter there that morning; his daughter was buckled into one of the Escalade’s seats. I was struck by how tiny the child looked inside the three-ton vehicle, how challenging it would be for her to clamber down to the ground outside.

The hulking white automobile was brand new, still without license plates. Why an Escalade? I asked. “It’s perceived to be safe,” he replied. “You know, more mass.”

More mass. The phrase kept playing on my mind as I walked back home. Whose safety was secured by all the vehicular mass hurtling down American roads, and at whose expense?

The rise of the SUV in global automotive markets is the second largest cause of increasing carbon emissions over the last decade, more significant than shipping, aviation and heavy industry. And at an everyday scale, there are serious consequences for those who encounter them in collisions.

Because of their rigid and heavy frames, SUVs and trucks are far more dangerous than conventional sedans for the pedestrians, cyclists and children at play who share American streets with automobiles. Pedestrian deaths on roadways in the United States have soared by more than 50% over the last decade.

Someone in an armored cockpit, someone else on their own two feet: this too is a polarized encounter. Low-income Americans and people of color are much more likely to be struck and killed while walking, which brings home another difficult truth in these developments.

Indifference is a privilege. Some can afford to seal themselves off from the world beyond, while those left outside must fend for themselves as best they can.

The fortress mindset thrives on suspicion, and the urge to protect oneself can make shared spaces and resources seem more dangerous than they are. Take that necessity for life itself, the water we drink. American consumers now buy an astounding 75 billion disposable bottles of water each year, each a tiny enclosure of an essential resource, a shelter made for one. The bottled water industry has capitalized on widespread unease about the quality of public water supplies in the United States. Meanwhile, as interest and investment in shared public infrastructure lags, people are left with polluted and contaminated water, forced to rely on bottled alternatives.

Two years before the pandemic began, I attended a bottled water trade show in Texas. Most everyone walked around with a small disposable bottle in hand, always closed, the little caps screwed back on after every sip. “I don’t drink public water,” people would avow, wrinkling their noses in distaste at the very idea of a drinking fountain. “Someone else’s mouth is on it and over it.”

Water fountains were switched off across the country in 2020 when the pandemic struck. But they’d already been disappearing for years, and how many will return remains uncertain. Bottled water is regulated so loosely that its quality is difficult to judge. Yet many Americans have come to believe again in the purity of a resource untouched by the wrong people, a dark contemporary echo of the segregated fountains of the Jim Crow era.

At the bottled water trade show, I spoke with a middle-aged white man in a brown suit who worked for a water conditioning company in west Texas. I noticed his habit of crumpling up each disposable bottle into a little ball when it was empty, and I asked him about this gesture.

“I like to put things away,” he told me, describing how he’d throw these crinkled balls of plastic into the back of his SUV while he was driving. I imagined them piling up in heaps, a travelling signpost for the mountain of waste that all of us are building together.

There’s a curious resonance between this faith in a sealed bottle, and a culture that celebrates the invulnerable body. Americans are often encouraged to imagine their own bodies as armored enclosures, to seal off against the outside world. Think of bottled sports drinks like BodyArmor or BioSteel. “Your body, your fortress,” their taglines read.

The coronavirus pandemic has supercharged such ideas, setting off a boom in personal disinfectant products and touchless technology, making it easier to deny the truth that we depend on each other for our wellbeing. The deep resistance to face masks and vaccination in the United States also relies, quite often, on a highly individualized sense of bodily autonomy.

I think of a middle-aged white businessman from Michigan with whom I’ve debated the pandemic for many months. A staunch libertarian, he considers compulsory public health precautions as tantamount to slavery. They deny, he says, “my feelings, my rights, my personal body”.

Regular exposure to different points of view could complicate such diehard convictions. But our fractured media have deepened the existing fissures of American society.

Walls at home and on the road, shielding the body from exposure and the mind from uncomfortable ideas: these interlocking divides make it more difficult to take unfamiliar people and perspectives seriously; harder to acknowledge the needs of strangers, to trust their motives and empathize with their struggles. In an atomized society, others become phantoms all too easily, grist for the mill of resentment and mistrust.

There’s a deep and pernicious history at work here. Longstanding patterns of neighborhood racial segregation have inflamed the prejudice against outgroups, bolstering stereotypes, as the political scientist Ryan Enos and others have shown. When such divisions are reproduced at an everyday scale, the gulf between self and other widens even further, and everyone becomes a potential outsider.

But this isn’t all that is happening, or could yet happen.

Around the country in 2020, the pandemic spurred a return to socializing with neighbors on front yards and porches. Cities and towns have carved out new places for walking, biking and outdoor life, new ways of sharing public space with people, known and unknown. It remains to be seen whether these are temporary adjustments or more enduring experiments.

Movements for mutual aid, racial justice and cultural solidarity have also brought Americans together, spurring more radical commitments to collective care-taking, redrawing the line between stranger and kin. The vitality of such movements depends on adequate space and support.

Calls abound to redesign our personal and public spaces for conviviality rather than isolation. Commons, parks and open streetscapes; living quarters and resources arranged to encourage social awareness, not solipsism; communication platforms that nurture contrary lines of thought: these spaces can nurture the capacity to live and thrive alongside others unlike oneself, working against the tendency to reject and retreat.

Our feelings for others are structural realities as much as personal qualities. In a society built on walls of indifference, empathy will remain an elusive hope. For “the death of the heart” is one of the most tragic consequences of segregation, as James Baldwin observed: “You don’t know what’s happening on the other side of the wall.”