For whatever reason or reasons, the United States has made it their policy over the last two generations to incarcerate more and more Americans, and is distinctly an outlier to all other western nations in regards to the per capita amount of Americans so incarcerated. It would be one thing if because of all the people that are currently incarcerated, or on probation, or on parole, this somehow made America the safest nation in the world, but that isn't true.
Further to the point, the incarceration rate in America is extraordinarily high, though it has come down off of its peak so that in 2016 as reported by pewresarch.org the United States had, "a nationwide incarceration rate of 860 prison or jail inmates for every 100,000 adults," which is an incarceration decline of about 14% from the cumulative years of 2006-2008. However, the amount of people being arrested in the year 2016, as compared to the years 2006-2008, has an even high rate of decline, in which as reported by statista.com, there were 10,662,552 arrests in 2016, as opposed to an average of 14,198,450 arrests in 2006-2008, or a decline of about 25% in arrests; signifying that while arrests are down, the relationship between arrests and incarceration has actually increased significantly in the interim.
While there are a few possible reasons as to why even with arrests being down, that incarceration rates have not come down in lockstep with that, the most obvious reason why this is so, is that the prosecutorial office, is basically the sole determinate as to whether a person so being arrested is actually prosecuted. This signifies, that even though, there have been less arrests in aggregate to prosecute from, prosecutors have simply dropped less cases, and thereby prosecuted through trial or plea bargain, a higher percentage of those so arrested.
The main reason why prosecutors are so eager to prosecute and convict arrestees of crimes, has little or nothing to do, with making the streets safer for good citizens, and a lot more to do with padding their statistics, so that they look like that they are tough on crime, for being tough on crime, is a very typical touchstone that plays well with the electorate, for these prosecutors for state and county are almost always subject to a democratic vote of the electorate, and the perceptions of those voters do matter.
What this means in effect, is that the lowest lying fruit, of which, these are typically people of color and/or impoverished, are in a very poor position to negotiate or to plead their way out of whatever offense or offenses that they are so accused of. Basically, all those that are reduced to having to utilize an overburden public defender, are effectively going to be convicted of something, in more cases than not, because prosecutors will take the police officer's arrest record information and then construct their charges in a manner that will trump up those charges into multiple and more serious charges, so as to bargain from a position of incredible strength, and thereby get the defendant to plea guilty to a lesser charge and subsequently rack up another win in their prosecutorial record.
All of this is basically a miscarriage of justice, for prosecutors are supposed to follow Constitutional law, which specifically entails equal justice which is equally applied, in addition to taking into account exculpatory evidence, and the legality of all evidence so obtained. In point of fact, prosecutors pretty much do whatever that they wish to do, recognizing that there is typically no independent authority that oversees how they conduct their business and what decisions that they so make. It is that prosecutorial discretion that is the predominate reason why incarceration rates are so high, for most arrestees are essentially considered to be chattel property for the prosecutors to do with as they so will.