Why is there so much shooting and killing in Chicago?

Chicago Tribune:

A day after Chicago’s weekend from hell, when outbreaks of gunfire killed 12 people and injured at least 62, the carnage continued.
Derrick Hall, 22, was waiting for a bus in the 9100 block of South Cottage Grove Avenue on Monday morning when a man approached and shot him to death, the Tribune reported. In the afternoon, three men were shot on West Iowa Street in South Austin. Later, a man was shot in the wrist by someone in a passing car. A man was hit in the stomach. A man was struck while getting into a vehicle. At least 10 people were shot in eight incidents Monday on the South and West sides.