Welcome to Rio de Janeiro. Late August 2020. A woman tries to keep her child quiet. She is using her phone to film silhouettes moving past her glass front door. There is no mistaking the swift, purposeful shadows. Hunkering down, they point assault rifles and machine guns. During the short, chilling clip at least nine men run past. They are so-called “drug soldiers” from one of Rio’s famous favela communities, in the process of invading another. The invasion led to hours of gun battles, hostage-taking incidents and the death of Ana Cristina da Silva, a 25-year-old mother (not the woman in the clip), as she protected her toddler from bullets. It took place a short walk from the business district and was the latest episode in the city’s four-decades-old “drug war,” one of the world’s most intractable urban armed conflicts. Millions—a quarter of cariocas (Rio residents)—live in more than a thousand favelas in metropolitan Rio. Heartbreakingly, these tight-knit micro-societies are some of the most violent urban areas in the world. Essentially, endemic violence serves to …