IN THE 1990s John DiIulio, a conservative American academic, argued that a new breed of “superpredators”, “kids that have absolutely no respect for human life and no sense of the future”, would terrorise Americans almost indefinitely. He was not alone. Experts were convinced that crime would keep rising. Law-abiding citizens would retreat to gated communities, patrolled by security guards. Politicians and police chiefs could do little except bluster and try to fiddle the statistics.

Mr DiIulio later recanted and it is clear that the pessimists were wrong. Even as he wrote, America’s crime wave was breaking. Its cities have become vastly safer, and the rest of the developed world has followed. From Japan to Estonia, property and people are now safer than at almost any time since the 1970s (see article). Confounding expectations, the recession has not interrupted the downward trend. Even as America furiously debates the shooting of Trayvon Martin (see article), new data show that the homicide rate for young Americans is at a 30-year low.

Some crimes have all but died out. Last year there were just 69 armed robberies of banks, building societies and post offices in England and Wales, compared with 500 a year in the 1990s. In 1990 some 147,000 cars were stolen in New York. Last year fewer than 10,000 were. In the Netherlands and Switzerland street dealers and hustlers have been driven out of city centres; addicts there are now elderly men, often alcoholics, living in state hostels. In countries such as Lithuania and Poland the gangsters who trafficked people and drugs in the 1990s have moved into less violent activities such as fraud.

The receding tide

Cherished social theories have been discarded. Conservatives who insisted that the decline of the traditional nuclear family and growing ethnic diversity would unleash an unstoppable crime wave have been proved wrong. Young people are increasingly likely to have been brought up by one parent and to have played a lot of computer games. Yet they are far better behaved than previous generations. Left-wingers who argued that crime could never be curbed unless inequality was reduced look just as silly.

There is no single cause of the decline; rather, several have coincided. Western societies are growing older, and most crimes are committed by young men. Policing has improved greatly in recent decades, especially in big cities such as New York and London, with forces using computers to analyse the incidence of crime; in some parts of Manhattan this helped to reduce the robbery rate by over 95%. The epidemics of crack cocaine and heroin appear to have burnt out.

The biggest factor may be simply that security measures have improved. Car immobilisers have killed joyriding; bulletproof screens, security guards and marked money have all but done for bank robbery. Alarms and DNA databases have increased the chance a burglar will be caught. At the same time, the rewards for burglary have fallen because electronic gizmos are so cheap. Even small shops now invest in CCTV cameras and security tags. Some crimes now look very risky—and that matters because, as every survey of criminals shows, the main deterrent to crime is the fear of being caught.

Loosen the cuffs

Many conservatives will think this list omits the main reason crime has declined: the far harsher prison sentences introduced on both sides of the Atlantic over the past two decades. One in every hundred American adults is now in prison. This has obviously had some effect—a young man in prison cannot steal your car—but if tough prison sentences were the cause, crime would not be falling in the Netherlands and Germany, which have reduced their prison populations. New York’s prison population has fallen by a quarter since 1999, yet its crime rate has dropped faster than that of many other cities.

Harsh punishments, and in particular long mandatory sentences for certain crimes, increasingly look counterproductive. American prisons are full of old men, many of whom are well past their criminal years, and non-violent drug users, who would be better off in treatment. In California, the pioneer of mandatory sentencing, more than a fifth of prisoners are over 50. To keep each one inside costs taxpayers $47,000 a year (about the same as a place at Stanford University). And because prison stresses punishment rather than rehabilitation, most of what remains of the crime problem is really a recidivism issue. In England and Wales, for example, the number of first-time offenders has fallen by 44% since 2007. The number with more than 15 convictions has risen.

Politicians seem to have grasped this. In America the number of new mandatory sentences enacted by Congress has fallen. Even in the Republican South, governors such as Rick Perry and Bobby Jindal have adopted policies favouring treatment over imprisonment for drug users. Britain has stopped adding to its prison population. But more could be done to support people when they come out of prison (at the moment, in Britain, they get £46) and to help addicts. In the Netherlands and Switzerland hard-drug addiction is being reduced by treatment rather than by punishment. American addicts, by contrast, often get little more than counselling.

Policing can be sharpened, too—and, in an era of austerity, will have to be. Now that officers are not rushed off their feet responding to car thefts and burglaries, they can focus on prevention. Predictive policing, which employs data to try to anticipate crime, is particularly promising. More countries could use civilian “community support officers” of the sort employed in Britain and the Netherlands, who patrol the streets, freeing up better-paid police officers to solve crimes.

Better-trained police officers could focus on new crimes. Traditional measures tend not to include financial crimes such as credit-card fraud or tax evasion. Since these are seldom properly recorded, they have not contributed to the great fall in crime. Unlike rapes and murders, they do not excite public fear. But as policing adapts to the technological age, it is as well to remember that criminals are doing so, too.