The story of how this decline came to be is quite complex, but one thing the Times story gets right is that these neighborhoods declined sharply when the middle class moved out to the suburbs. The article recounts the experience of one of the residents:
Ms. Gordon has seen a diverse middle-class neighborhood of white and black families transform into one of abandoned, overgrown lots and boarded-up houses. As in many downtrodden parts of St. Louis, the middle class fled for the suburbs, leaving behind those with less economic mobility and causing property values to drop, the education system to crumble and feeding a sense of desperation that leads people to sell drugs and steal.
Read more: http://blog.acton.org/archives/62782-cities-need-black-middle-class.html