The Supreme Court sided with a prison inmate in its decision in Millbrook v. United States. Reuters

Almost a quarter of the world’s prison population is locked up in one country: the United States.

For years, the U.S. has held the infamous reputation of having the highest per capita rate of incarcerated individuals on the planet, dwarfing that of other comparable industrialized nations. There were 1.6 million state and federal prisoners in the country as of 2011, according to the Bureau of Justice Statistics, which reports 492 out of every 100,000 U.S. residents were sentenced to more than 12 months in prison that year.

After a year of persistent increases, the U.S. Justice Department in December reported the number of adults in state and federal prisons had finally declined from 2010 and 2011 level. That primarily occurred after 26 states, led by California, each shed at least 1,000 state prisoners to combat overcrowding and rein in costs.

But the federal prison population continues to grow. An average of 6,100 inmates have entered the system each year since 1980, according to the Congressional Research Service (CRS), which reports there were about 219,000 inmates under federal Bureau of Prison’s (BOP) jurisdiction in 2012 -- a nearly 790 percent increase in 32 years.

The escalating number of federal prisoners, combined with the rising per capita cost of incarceration – the result of increasing utility, food and medical costs – had made it considerably more expensive to even maintain federal prisons. Between 2000 and 2011 alone, appropriations for the BOP almost doubled, from $3.6 billion to $6.3 billion.

Most Federal Prisoners Arrested For Drug Crimes

The sad part is, most of that money has been used to lock up drug offenders.

Since 1998, individuals arrested for drug crimes have constituted the largest portion of federal prison admissions, followed closely by those arrested for immigration and weapons-related offenses. Meanwhile, the CRS reports there has been a significant drop off in the number of inmates entering prison for violent or property-related crimes, which only made up about 4 percent and 11 percent of prison admissions in 2010.

A huge portion of those drug offenders are arrested for marijuana offenses, even though the substance – now legal in 18 states for medicinal use– has become increasingly mainstream. However, statistics from the Federal Bureau of Investigation reveal more people were arrested for marijuana possession than all violent crimes combined in 2011.

If it continues to grow at the same rate, the Urban Institute predicts the federal prison system will eat up as much as 30 percent of the Department of Justice’s budget by 2020. The group reports the rapid population increase has mainly come from imposing longer sentences, and not a higher arrest rate. Drug offenders are often the targets of those sentences.

Mandatory Minimums Keep Inmates Behind Bars

The growth of federal prisoners can be attributable to three main policy changes that have occurred since 1980: increasing the number of federal offenses subject to mandatory minimum sentences, expanding the federal criminal code to make more crimes federal offenses, and eliminating parole.

The United States Sentencing Commission has acknowledged that the enactment of federal mandatory minimum sentences has, in part, contributed to the skyrocketing prison rate. The number of mandatory minimums in the federal criminal code nearly doubled from 98 to 195 between 1991 and 2011, while offenders convicted of offenses with those mandatory minimums are being sent to prison for longer periods of time.

Those stricter penalties are even affecting inmates who have not been arrested for a crime with a mandatory sentence attached.

“While only offenders convicted for an offense carrying a mandatory minimum penalty are subject to those penalties, mandatory minimum penalties have, in effect, increased sentences for other offenders,” the CRS explains. “The USSC has incorporated many mandatory minimum penalties into the sentencing guidelines, which means that penalties for other offense categories under the guidelines had to increase in order to keep a sense of proportionality.”

To work around the prevalence of mandatory minimums, the CRS suggests lawmakers could consider expanding the “safety valve” provision of the United States Code, which allows judges to impose a sentence without regard to the mandatory minimum sentences for certain drug offenses (in cases where the defendant does not have a criminal history and whose crime did not include violent acts).

Reducing the scope of federalized offenses could also help lower the federal prison rate by allocating more jurisdiction to state authorities, particularly for some drug and firearm offenses.

No Parole For Federal Prisoners

Federal prisoners do not have the ability to receive parole, when correctional authorities release low-risk inmates into community supervision for the remainder of their sentences.

Inmates sentenced after November 1, 1987 are no longer eligible for parole, meaning every offender sentenced since then must serve the entirety of his or her sentence. As a result, there have not been enough prisoners released to make way for new inmates as federal sentencing rates ballooned in the 1990s and early 2000s.

“Data from the BOP indicates that nearly three-quarters of inmates have served at least 25 percent of their sentence, meaning that if Congress reinstated the old parole eligibility rules, a majority of federal inmates would be eligible for parole consideration,” the CRS reports.

The research service, noting that the release of federal prisoners could be framed as a threat to public safety, highlighted the importance of investing in rehabilitation programs that not only help inmates adjust to the outside world, but can – in the case of many drug offenders – help them overcome the very addiction that landed them in prison.

“A review of the literature on rehabilitative programs (e.g., academic and vocational education, cognitive-behavioral programs, and both community-and prison-based drug treatment) suggests that there are enough scientifically sound evaluations to conclude that they are effective at reducing recidivism [the rate at which released inmates are rearrested], which could potentially help stem growth in the federal prison population in the future,” the CRS reports