It's been around forever, right?
For most of history, imprisoning has not been a punishment in itself, but rather a way to confine criminals until corporal or capital was administered. Only in the 19th century, beginning in Britain, did prisons as we know them today become commonplace. The modern prisons system was born in London, as a result of the views of Jeremy Bentham. The notion of prisoners being incarcerated as part of their punishment and not simply as a holding state until trial or hanging, was at the time revolutionary.
It deters people, right?
Meta-analysis shows that prison sentences do not reduce future offenses, when compared to non-residential sanctions. This meta-analysis of one hundred separate studies found that post-release offenses were around 7% higher after imprisonment compared with non-residential sanctions, at statistically significant levels. Longer periods of time in prison make outcomes worse, not better; offending increases by around 3% as prison sentences increase in length.
It's only for pretty bad people, right?
As of 2006, it is estimated that at least 9.25 million people are currently imprisoned worldwide.
The leader in just about everything...
In absolute terms, the United States currently has the largest inmate population in the world, with more than 2½ million or more than one in a hundred adults in prison and jails. Although the United States represents less than 5% of the world's population, over 25% of the people incarcerated around the world are housed in the American prison system.
Approximately half of the U.S. jail population consists of pretrial detainees who have not been convicted or sentenced.