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One fall evening in 2020, Jarell Jackson and Shahjahan McCaskill were chatting in Jackson’s Hyundai Sonata, still on a postvacation high, when 24 bullets ripped through the car. The two men, both 26, had been close friends since preschool. They’d just returned to West Philadelphia after a few days hang gliding, zip-lining, and hiking in Puerto Rico. Jackson was parked outside his mom’s house when a black SUV pulled up and the people inside started shooting. Both he and McCaskill were pronounced dead at the hospital.

In the aftermath, McCaskill’s mother, Najila Zainab Ali McCaskill, couldn’t fathom why anyone would want to kill her son and his friend. Both had beaten the odds for young Black men in their neighborhood and graduated from college. Jackson had been a mental-health technician in an adolescent psych ward while her son had run a small cleaning business and tended bar. She wondered if they’d been targeted by a disgruntled former employee of the cleaning business. But then the police explained: Her son and his friend had been killed because of a clash on social media among some teenagers they’d never even met.

For months, a battle had been raging on Instagram between crews based on either side of Market Street. Theirs was a long-running rivalry, but a barrage of online taunts and threats had raised tensions in the neighborhood. Police had assigned an officer to monitor the social-media activity of various crews in the city, and the department suspected that the Northsiders in the SUV had mistaken one of the two friends for a rival Southsider and opened fire. An hour after the shooting, a Northsider posted a photo on Instagram with a caption that appeared to mock the victims and encourage the rival crew to collect their bodies: “AHH HAAAA Pussy Pick Em Up!!”

Jackson and McCaskill died in the first year of a nationwide resurgence in violence that has erased more than two decades of gains in public safety. In 2020, homicides spiked by 30 percent and fluctuated around that level for the next two years. There are early signs that the 2023 rate could show a decrease of more than 10 percent from last year, but that would still leave it well above pre-pandemic levels.

Criminologists point to a confluence of factors, including the social disruptions caused by COVID‑19, the rise in gun sales early in the pandemic, and the uproar following the murder of George Floyd, which, in many cities, led to diminished police activity and further erosion of trust in the police. But in my reporting on the surge, I kept hearing about another accelerant: social media.

Violence-prevention workers described feuds that started on Instagram, Snapchat, and other platforms and erupted into real life with terrifying speed. “When I was young and I would get into an argument with somebody at school, the only people who knew about it were me and the people at school,” said James Timpson, a violence-prevention worker in Baltimore. “Not right now. Five hundred people know about it before you even leave school. And then you got this big war going on.”

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Smartphones and social platforms existed long before the homicide spike; they are obviously not its singular cause. But considering the recent past, it’s not hard to see why social media might be a newly potent driver of violence. When the pandemic led officials to close civic hubs such as schools, libraries, and rec centers for more than a year, people—especially young people—were pushed even further into virtual space. Much has been said about the possible links between heavy social-media use and mental-health problems and suicide among teenagers. Now Timpson and other violence-prevention workers are carrying that concern to the logical next step. If social media plays a role in the rising tendency of young people to harm themselves, could it also be playing a role when they harm others?

The current spike in violence isn’t a return to ’90s-era murder rates—it’s something else entirely. In many cities, the violence has been especially concentrated among the young. The nationwide homicide rate for 15-to-19-year-olds increased by an astonishing 91 percent from 2014 to 2021. Last year in Washington, D.C., 105 people under 18 were shot—nearly twice as many as in the previous year. In Philadelphia in the first nine months of 2022, the tally of youth shooting victims—181—equaled the tally for all of 2015 and 2016 combined. And in Baltimore, more than 60 children ages 13 to 18 were shot in the first half of this year. That’s