There are several causes:

Drugs - Meth, Heroin, Coke, & Crack
Poor Education System
Media induced thug culture
Media induced disgusting culture
No structure in society, it is all shades of gray for young people
No jobs for those that are not rocket scientists - those jobs went overseas and the greedy American's sold out their people for cheap, poor quality goods. Hogs to the trough.
An evil legal system that preys upon young people that took the bait put out by the media and the culture
Mandatory Minimums, sentencing is a one size fits all rather than the judge looking at the circumstances and the person

Fuck this place and the dumb fucking laws and dumb fucking jurors that put people away for years on end. I don't like Obama and his gang but I have to say he is doing one hell of job on destroying this place. However, he could not have done it if the people were not so damn evil.