Last year, mass shootings accounted for just two per cent of American gun deaths. Most gun violence is impulsive and up close. Photograph by Dan Winters for The New Yorker

Bars in the Old City neighborhood of Philadelphia let out at 2 A.M. On the morning of January 17, 2010, two groups emerged, looking for taxis. At the corner of Market and Third Street, they started yelling at each other. On one side was Edward DiDonato, who had recently begun work at an insurance company, having graduated from Villanova University, where he was a captain of the lacrosse team. On the other was Gerald Ung, a third-year law student at Temple, who wrote poetry in his spare time and had worked as a technology consultant for Freddie Mac. Both men had grown up in prosperous suburbs: DiDonato in Blue Bell, Pennsylvania, outside Philadelphia; Ung in Reston, Virginia, near Washington, D.C.

Everyone had been drinking, and neither side could subsequently remember how the disagreement started; one of DiDonato’s friends may have kicked in the direction of one of Ung’s friends, and Ung may have mocked someone’s hair. “To this day, I have no idea why this happened,” Joy Keh, a photographer who was one of Ung’s friends at the scene, said later.

The argument moved down the block, and one of DiDonato’s friends, a bartender named Thomas V. Kelly IV, lunged at the other group. He was pushed away before he could throw a punch. He rushed at the group again; this time, Ung pulled from his pocket a .380-calibre semiautomatic pistol, the Kel-Tec P-3AT. Only five inches long and weighing barely half a pound, it was a “carry gun,” a small, lethal pistol designed for “concealed carry,” the growing practice of toting a hidden gun in daily life. Two decades ago, leaving the house with a concealed weapon was strictly controlled or illegal in twenty-two states, and fewer than five million Americans had a permit to do so. Since then, it has become legal in every state, and the number of concealed-carry permit holders has climbed to an estimated 12.8 million.

Ung had obtained a concealed-carry license because he was afraid of street crime. He bought a classic .45-calibre pistol but later switched to the Kel-Tec, which was easier to carry; for a year and a half, he stowed one of the pistols in his pocket or in his backpack. He had never fired it. Now, on the sidewalk, he held the Kel-Tec with outstretched arms. A pedestrian heard him yell, “You’d better not piss me off!” Ung maintains that he said, “Back the fuck up.” DiDonato thought the pistol looked too small to be real; he guessed that it was a BB gun. He spread his arms, stepped forward, and said, “Who are you going to shoot, man?” Ung pulled the trigger. Afterward, he couldn’t recall how many times—he said it felt like a movie, and he was “seeing sparks and hearing pops.”

Ung hit DiDonato six times: in the liver, the lung, the shoulder, the hand, the intestine, and the spine. When DiDonato collapsed, Ung called 911 and said that he had shot a man. On the call, he was recorded pleading, “Why did you make me do it?” DiDonato, in a weak voice, can be heard saying, “Please don’t let me die.” When police arrived, Ung’s first words were “I have a permit.”

More American civilians have died by gunfire in the past decade than all the Americans who were killed in combat in the Second World War. When an off-duty security guard named Omar Mateen, armed with a Sig Sauer semiautomatic rifle and a Glock 17 pistol, killed forty-nine people at a gay club in Orlando, on June 12th, it was historic in some respects and commonplace in others—the largest mass shooting in American history and, by one count, the hundred-and-thirtieth mass shooting so far this year. High-profile massacres can summon our attention, and galvanize demands for change, but in 2015 fatalities from mass shootings amounted to just two per cent of all gun deaths. Most of the time, when Americans shoot one another, it is impulsive, up close, and apolitical.

None of that has hurt the gun business. In recent years, in response to three kinds of events—mass shootings, terrorist attacks, and talk of additional gun control—gun sales have broken records. “You know that every time a bomb goes off somewhere, every time there’s a shooting somewhere, sales spike like crazy,” Paul Jannuzzo, a former chief of American operations for Glock, the Austrian gun company, told me.

Sometimes the three sources of growth converge. On November 13th of last year, terrorists in Paris killed a hundred and thirty people and wounded hundreds more. On December 2nd, a husband and wife, inspired by ISIS, killed fourteen people in San Bernardino, California. This year, on January 5th, President Obama announced executive actions intended to expand the use of background checks. By the end of that day, the share price of Smith & Wesson, the largest U.S. gunmaker, had risen to $25.86, its highest level ever. After the attack in Orlando, shares of Smith & Wesson rose 9.8 per cent before the market opened the next day. Last week, the company reported that, in its latest fiscal year, revenue grew thirty-one per cent, to a record $733 million. In a call with investors and analysts, Smith & Wesson’s C.E.O., James Debney, said that he was “very pleased with the results that we got.” He attributed the growth in firearm sales to “increased orders for our handgun designed for personal protection.”

The story of how millions of Americans discovered the urge to carry weapons—to join, in effect, a self-appointed, well-armed, lightly trained militia—begins not in the Old West but in the nineteen-seventies. For most of American history, gun owners generally frowned on the idea. In 1934, the president of the National Rifle Association, Karl Frederick, testified to Congress, “I do not believe in the promiscuous toting of guns. I think it should be sharply restricted and only under licenses.” In 1967, after a public protest by armed Black Panthers in Sacramento, Governor Ronald Reagan told reporters that he saw “no reason why on the street today a citizen should be carrying loaded weapons.”

But the politics of guns and fear were changing. In 1972, Jeff Cooper, a firearms instructor and former marine, published “Principles of Personal Defense,” which became a classic among gun-rights activists and captured a generation’s anxieties. “Before World War II, one could stroll in the parks and streets of the city after dark with hardly any risk,” he wrote. But in “today’s world of permissive atrocity” it was time to reëxamine one’s interactions with fellow-citizens. He ticked off the names of high-profile killers, including Charles Manson, and wrote of their victims, “Their appalling ineptitude and timidity virtually assisted in their own murders.” Adapting a concept from the Marines, he urged civilian gun owners to assume a state of alertness that he called Condition Yellow. He wrote, “The one who fights back retains his dignity and his self-respect.”

Soon armed citizens acquired a political voice: in 1977, at the N.R.A.’s annual meeting, conservative activists led by Harlon Carter, a former chief of the U.S. Border Patrol, wrested control from leaders who had been focussed on rifle-training and recreation rather than on politics, and created the modern gun-rights movement. In 1987, the refashioned N.R.A. successfully lobbied lawmakers in Florida to relax the rules that required concealed-carry applicants to demonstrate “good cause” for a permit, such as a job transporting large quantities of cash.