America is different from the rest of the world in lots of ways, many of them good. One of the bad ones is its willingness to lock up its citizens. One American adult in 100 festers behind bars (with the rate rising to one in nine for young black men). Its imprisoned population, at 2.3m, exceeds that of 15 of its states. No other rich country is nearly as punitive as the Land of the Free. The rate of incarceration is a fifth of America's level in Britain, a ninth in Germany and a twelfth in Japan. America's incarceration rate has quadrupled since 1970. Similar things have happened elsewhere. The incarceration rate in Britain has more than doubled, and that in Japan increased by half, over the period. But the trend has been sharper in America than in most of the rich world, and the disparity has grown. It is explained neither by a difference in criminality (the English are slightly more criminal than Americans, though less murderous), nor by the success of the policy: America's violent-crime rate is higher than it was 40 years ago. Many states have mandatory minimum sentences, which remove judges' discretion to show mercy, even when the circumstances of a case cry out for it. Three strikes" laws, which were at first used to put away persistently violent criminals for life, have in several states been applied to lesser offenders.