Economist Glen Loury writes on Will Wilkinson's Cato Unbound:

A Nation of Jailers

I wish to discuss a preeminent moral challenge for our time – that imprisonment on a massive scale has become one of the central aspects of our nation’s social policy toward the poor, powerfully impairing the lives of some of the most marginal of our fellow citizens, especially the poorly educated black and Hispanic men who reside in large numbers in our great urban centers. ...

Here, as in other areas of social policy, the United States is a stark international outlier, sitting at the most rightward end of the political spectrum: We imprison at a far higher rate than the other industrial democracies ...

The demographic profile of the inmate population has also been much discussed. In this, too, the U.S. is an international outlier. African Americans and Hispanics, who taken together are about one fourth of the population, account for about two thirds of state prison inmates.

I think, Glenn, that if you stop and think about it, you'll see that you kinda answered your own question right there. (The other differences are that America has way more guns that Europe so more people wind up dead in altercations and the other parties spend longer in prison. Also, the U.S. is tougher on things like burglary and assault and battery, so we have a lot less of it than, say, Britain when adjusted for race.)

The extent of racial disparity in imprisonment rates exceeds that to be found in any other arena of American social life: at eight to one, the black to white ratio of male incarceration rates dwarfs the two to one ratio of unemployment rates, the three to one non-marital child bearing ratio, the two to one ratio of infant mortality rates and the one to five ratio of net worth.

Actually, there is one other arena where the racial disparity ratio is the same as in imprisonment: in committing crimes.

James Q. Wilson wrote:

Estimating the crime rates of racial groups is, of course, difficult because we only know the arrest rate. If police are more (or less) likely to arrest a criminal of a given race, the arrest rate will overstate (or understate) the true crime rate. To examine this problem, researchers have compared the rate at which criminal victims report (in the National Crime Victimization Survey, or NCVS) the racial identity of whoever robbed or assaulted them with the rate at which the police arrest robbers or assaulters of different races. Regardless of whether the victim is black or white, there are no significant differences between victim reports and police arrests. This suggests that, though racism may exist in policing (as in all other aspects of American life), racism cannot explain the overall black arrest rate. The arrest rate, thus, is a reasonably good proxy for the crime rate.

Black men commit murders at a rate about eight times greater than that for white men. This disparity is not new; it has existed for well over a century. When historian Roger Lane studied murder rates in Philadelphia, he found that since 1839 the black rate has been much higher than the white rate. This gap existed long before the invention of television, the wide distribution of hand guns, or access to dangerous drugs (except for alcohol).

Loury acts ignorant of the fact that America cut its imprisonment per crime rate sharply back in the later 1960s. There were more people in prison in 1960 than in 1970. How'd that work out for us?