The new Homicide Monitor, launched by Brazil’s Igarapé Institute, contains a familiar happy story: the decline of murder in the developed world. In 18 European countries, fewer than one person in 100,000 was murdered in 2012, says the monitor. These are around the lowest rates in recorded history. The most murderous regions today are Latin America and the Caribbean. But intriguingly, some of Latin America’s more developed cities are joining the rich world’s trend towards peacefulness. Rio de Janeiro’s homicide rate fell nearly two-thirds from 2002 to 2012. S?o Paulo’s dropped 80 per cent from 2000 to 2010.

Nobody can quite explain this. “We still barely understand why homicide rates have declined consistently across the western world over the past 20 years,” admits Manuel Eisner, criminologist at Cambridge university. The rise of screens may have helped: nowadays many violence-prone young males spend their days on WhatsApp or PlayStation. But Eisner and other thinkers suggest another fascinating explanation: starting in the early 1990s, western countries entered an age of restraint. Our generation has chosen safety over freedom. This explanation sounds impossibly grand, yet it’s plausible.

Many forms of disorder besides homicide have declined in the west since the 1990s. A few examples: the European Union’s total crime rate has been “steadily decreasing since 2003”, reports the European Commission. Perhaps coincidentally, the EU experienced “a marked decrease in recorded adult per capita alcohol consumption” from 1990 through 2010, says the World Health Organisation. Reduced drinking has helped reduce western traffic deaths. And the US National Crime Victimization Survey, which asks Americans whether they have experienced crime, shows among other good things a 64 per cent fall in sexual violence against women from 1995 through 2010. (The violence and disorder in poorer countries, from Syria to Honduras, is an entirely different story.)