The United States has 5% of the world's population and 25% of the world's prisoners. More than Russia. More than China. 2.2 Million prisoners and counting.
I refer you to the book Gates of Injustice
by Alan Elsner, a reporter for Reuters, for a detail examination of this topic.
USA - 702 out of 100,000 persons are in prison
Russia - 628 out of 100,000 are incarcerated.
United Kingdom - 138 out of 100,000
France - 138 out of 100,000
NOTE: in 1972, the USA only imprisoned 160 out of every 100,000 persons.
Why the sudden growth of the prison population? The biggest contributor is non-violent drug convictions, but that's a result, not a cause. The country COULD have been arresting large numbers of people for drug violations before 1972. It just didn't.
Sociologically, and here we leave the realm of fact, and enter the realm of total speculation, I think it's basically a reaction design to deprive the 'undeserving' of rights. The ability of the dominant social classes in the USA to exploit disadvantages classes was vastly curtailed during the 1960's. Millions of people couldn't get certain jobs, couldn't live in certain places, didn't get educated, had no recourse to the legal system. ANd all of this benefited the more advantaged classes.
By 1972, most of those kinds of discrimination were illegal. Provided you hadn't been convicted of a felony.
Replace 'non-white' with 'convict' and 'ex-convict', and voila! You have a legally exploitable underclass again. Google 'Prison Industrial Complex' and read a while. You'll see why some people say slavery is alive and well in America.
For profit companies hold people in chains and make them work them while taking the profit of their labor. Is that a definition of slavery? Or the modern American penal system?
2.2 million people is a country
. That's what the USA is holding imprisoned. In the United States. The USA actually operates prisons around the world, but they aren't included in these statistics.