The US prison system is absolutely terrible. We have a recidivism rate of 1/3, meaning 1 in every 3 released inmates end up back in jail in under a year. They focus much too heavily on the punitive (punishment) aspect of prison, and don't spend nearly enough time on rehabilitation.
The prison system is punishment-based. If you do this, you get x amount of years, etc. The government presumes that lengthy prison sentences are enough to deter crime, but that's because they're assuming that criminals who commit crimes are thinking logically and rationally at the time. And most aren't.
I think we need to change the way we think about "prison sentences". Instead of just locking people up and leaving them on their own, let's instead use that sentence to educate and prepare inmates for life upon release. If we can teach inmates coping methods on how to handle things like anger, not to mention if we helped with alcohol or drug problems, we could seriously reduce the amount of people who end up back in prison.