IN MAY 2015, Barack Obama barred the federal government from providing some military equipment to American police departments. The extraordinary arsenal maintained by some departments—which includes body armour, powerful weapons and armoured vehicles—had become highly visible over the previous year, as a result of outbreaks of unrest in response to police violence. In August 2014 Darren Wilson, a police officer, shot and killed Michael Brown, an unarmed 18-year-old black man in Ferguson, Missouri, sparking large local demonstrations. Two days after the shooting, tactical officers—paramilitary police generally referred to as SWAT (for Special Weapons and Tactics) teams—were called in to help clear protestors from in front of Ferguson's police department. They arrived dressed for war, in riot gear and gas masks, bearing long truncheons and automatic weapons. Americans have grown used to seeing police respond to protests with tear gas, carrying automatic weapons and sniper rifles, and riding in vehicles that would not look out of place in Baghdad or Aleppo. The days of the beat cop walking the street with nothing more than a trusty old revolver seem distant indeed. How did America's police forces become so heavily armed?
