There is an excellent article on the Atlantic today about mass incarceration in the US today and how the US is a global anomaly on this front in the West.
The article also stresses that mass incarceration s a fairly recent phenomenon. Consider the following chart:
As you can see, the phenomenon of mass incarceration began to take off in 1973 with the "War on Drugs," ballooning in the the subsequent decades under Reagan, Clinton, and both Bushes. The prison population in 2012 was almost ten times the average prison population from the post-war era (1945-1973).
It is interesting (and important) to see how the rise of mass incarceration mirrors the collapse of the post-war consensus, the steep rise in inequality, and the entrenchment of the neoliberal economic consensus.