What is the reason for the rapid inclination of incarceration rates in America?

Majority of which are non violent offenders. I mean in 1980 we had just under 500 thousand inmates incarcerated in America, now we have roughly 2.5 million. That is a staggering increase and I truly believe that the prison system needs a complete overhaul for tax and financial reasons. Also I do not see how housing so many non violent criminals is considered productive when they are surrounded by other criminals and are more likely to become "career criminals" by the time they get out. Sounds like a viscous cycle to me. What do you think is the reason for rapid inclination in inmates in Americas prison system is? Also what can we do to change this so tax payers aren't burdened by having to house all of these individuals. Here is a link to see the chart that goes to 2006 (the number of inmates have increased since then) http://upload.wikimedia.org/wikipedia/commons/thumb/5/54/US_incarceration_timeline-clean.svg/693px-US_incarceration_timeline-clean.svg.png.