The moment the assault rifles surrounded her, Angie Wong was standing in a leafy art-gallery courtyard with her boyfriend, a lawyer named Paul Kaiser. It was just past 2 A.M., in May, 2008. Wong was twenty-two years old and was dressed for an evening out, in crisp white jeans, a white top, and tall heels that made it difficult not to wobble. The couple had stopped by a regular event hosted by the Contemporary Art Institute of Detroit (CAID), a red brick gallery with the aim of “turning Detroit into a model city,” and arrived to find a tipsy, jubilant scene: inside, gallerygoers were looking at art and dancing to a d.j.; outside, on the patio, several young women were goofily belting out the lyrics to “Hakuna Matata,” from “The Lion King”:

Hakuna Matata! What a wonderful phrase.

It means no worries for the rest of your days.

It’s our problem-free philosophy. Hakuna Matata!

Only then did masked figures with guns storm the crowd, shouting, “Get on the fucking ground! Get down, get down!” (I document the basic details of what happened in my story, in this week’s magazine, about the police’s use and abuse of civil-asset-forfeiture laws.) Some forty Detroit police officers dressed in commando gear ordered the gallery attendees to line up on their knees, then took their car keys and confiscated their vehicles, largely on the grounds that the gallery lacked the proper permits for dancing and drinking. (More than forty cars were seized, and owners paid around a thousand dollars each to get them back.) “I was so scared,” Wong told me. At first, she thought the raid was an armed robbery. “Out of the corner of my eye, I could see Paul getting kicked in the face.” In the dimly lit security footage, the scene looks like something out of a thriller about Navy SEALs. Paul said, “I was scared for my life.”

In my magazine article, I focus on one key question about the raid, and about countless others like it across America: Does it make sense that civil-forfeiture laws, which allow police to confiscate and keep property that is allegedly tied to criminal activity, are often enforced at gunpoint against, say, nonviolent partygoers? But there’s another important question, highlighted by the operation at CAID: What, fundamentally, are SWAT teams for? When does it make sense to use machine guns, armored vehicles, and flash-bang grenades on a crowd of people or on a family, and how are these warfare-inspired approaches to law enforcement changing America?

In 1972, America conducted only a few hundred paramilitary drug raids a year, according to Michelle Alexander’s “The New Jim Crow: Mass Incarceration in the Age of Colorblindness.” By the early nineteen-eighties, there were three thousand a year; by 2001, Alexander notes, the annual count had skyrocketed to forty thousand. Today, even that number seems impossibly low; with one annual count of combat-style home raids hovers around eighty thousand. (The title of Alexander’s book reflects the racially disparate impacts of these policies.)

In some cases, the rationale for using military weapons and tactics on domestic soil seems obvious: look no further, proponents argue, than the recent hunt for the Tsarnaev brothers after the Boston Marathon bombings. But what’s remarkable is how routine these tactics have become as a means of pursuing nonviolent suspects and low-level investigations, particularly in the war on drugs. Thousands of police departments nationwide have recently acquired stun grenades, armored tanks, counterattack vehicles, and other paramilitary equipment, much of it purchased with asset-forfeiture funds. In addition, as ABC reports, a U.S. Department of Defense program, often called the Pentagon Pipeline, has redistributed billions of dollars’ worth of surplus military gear to local police forces, a significant portion of it repurposed from Iraq and Afghanistan. (For example, a Humvee was used to patrol a school campus.) These acquisitions have no doubt helped to transform full-scale, bust-down-the-door raids on homes and businesses from red-alert rarities, reserved for life-threatening scenarios, to commonplace occurrences.

Few people understand this change as well as Radley Balko, the author of a fascinating and at times wrenching new book, “Rise of the Warrior Cop: The Militarization of America’s Police Forces.” For years, Balko has been an incisive chronicler of the drug war. In the course of the past few months, on the Huffington Post, he’s featured the “raid of the day,” cataloguing examples of SWAT operations gone hauntingly wrong. (One involved an unarmed twenty-one-year-old named Trevon Cole, who was shot dead during a botched drug raid on his Las Vegas apartment; his name had been confused with that of another man. In another case, a forty-one-year-old computer engineer named Cheryl Ann Stillwell was killed during a SWAT raid in Florida, based on a tip alleging the sale of two Oxycontin pills.) Balko’s raid taxonomy seems almost endless, and, indeed, his book situates these violent incidents in a history that stretches back to the years preceding the American Revolution. The Founders, Balko notes, evinced a clear “wariness of standing armies … born of experience and a study of history,” and they designed the Constitution expressly to guard against the home raids, property seizures, and other routine indignities to which the Britain subjected its colonists. “If even the earlier attempts at centralized police forces would have alarmed the Founders, today’s policing would have terrified them,” Balko writes.

“This is not an anti-cop book,” Balko stresses more than once in “Rise of the Warrior Cop.” His point, rather, is that “systems governed by bad policies and motivated by incentives will produce bad outcomes.”

There is still a lot that we don’t know about what these policies and their outcomes look like. Transparency has been mostly lacking. In March, affiliates of the American Civil Liberties Union filed more than two hundred and sixty public-records requests in twenty-five states, seeking information from law-enforcement agencies and National Guard offices on how federal funding has helped to drive the militarization of local and state police departments. Kara Dansky, the senior counsel of the A.C.L.U.’s Center for Justice, told me that the resulting data have just begun to pour in, and many agencies have proved to be coöperative. The biggest surprise thus far, Dansky says, is how little uniformity and clarity there is about when officers are advised to use extreme SWAT tactics, particularly in cases where mentally ill or suicidal individuals are the targets. “One major trend that we’re seeing is that police departments across the country vary tremendously in terms of how, if at all, they document information pertaining to their SWAT deployments,” Dansky said. “We have very little doubt that there are circumstances where the use of military tactics or equipment would be an appropriate response to a domestic law-enforcement situation.… But there aren’t always clear standards in place for when certain tactics are appropriate.”