During some general reading on finance, I ran across the following two information-rich graphics from Hoya Capital on the U.S. prison population. On the first graph, the blue areas show the absolute numbers, and the green line shows the percent incarceration rate. A rate of 0.5% comes to 500 prisoners per 100,000 population.

This graph shows a huge rise in the state and federal prison population between 1980 and 2000. There seems general agreement that much of that increase in the prison population is due to mandatory sentencing laws, which require relatively long sentences. In particular, “three strikes and you’re out” laws may demand a life sentence for three felony convictions, if at least one of them is for a serious violent crime. Another factor was the increased criminalization of drug use (possession), in addition to drug dealing.
The graphic below shows the particular classes of crimes of which inmates of the state and federal prison systems have been convicted. The largest single category is violent crimes, but other types are significant, such as drug and property crimes, and “public order” crimes. Public order crimes include activities such as prostitution, gambling, alcohol, child pornography, and some drug charges. This graphic also includes the large number of people in local jails, most of whom are imprisoned awaiting trial or sentencing.

The total number of people under legal supervision in the U.S., including probation and parole, is over 6 million:

Source: Wikipedia
The U.S. has by far the largest official prison population in the world, and the highest incarceration rate. The following graph from Wikipedia depicts incarceration rates for several countries or regions as of 2009:

Most developed countries have incarceration rates of around 100-200 per 100,000, which is where the U.S. was in about 1970. The relatively high rate for Russia is attributed in large part to strict “zero tolerance” laws on drugs.
Again, the main driver for the high rates in the U.S. is the long sentences, driven by mandates. Wikipedia notes that there are other countries, including some in Europe, which have higher annual admissions to prison per capita than in the U.S. However, “The typical mandatory sentence for a first-time drug offense in federal court is five or ten years, compared to other developed countries around the world where a first time offense would warrant at most 6 months in jail… The average burglary sentence in the United States is 16 months, compared to 5 months in Canada and 7 months in England.”
Policy debates on this topic continue. Obviously, we want to protect society from dangerous predators, but the direct and indirect costs to society for this level of incarceration are high. It seems like an area which is ripe for reform of some kind, though I do not claim to have a novel proposal.