This was all fueled by lead poisoning

The decline of large cities into crime, violence and vandalism was seen the world over, and most of the places began to improve when lead was phased out as an additive in gasoline.

Some people have said that this is only a chance statistical correlation, but there is further explanation in that it's known that lead damages the part of the brain most responsible for impulse control. Lead posioning has been observed to lead to mental restlessness that a sufferer may attempt to alleviate through violent or destructive acts.

The people who credited with introducing new initiatives to turn things around hit lucky, if they had introduced then in 1980, they would likely have not worked very well.

It's one of the biggest man made disaster ever, many people raped, robbed, assaulted, murdered - did you know companies making the lead additives used bribery to keep them in use.