Russia and USA House More Inmates than All European Countries Combined

The Pew project has very interesting data on incarceration per capita. USA houses more inmates than the top 35 European countries combined. Russia is in the second place. Another interesting fact is that the top ten, except USA, represents the former Soviet countries. Also, I am surprized that dwarf-countries like Georgina, Estonia, Latvia, and Lithuania are in the top ten. What are the causes? It could be that the FSU countries and USA have higher crime rate than European countries. It could be that the law and enforcement is more effective in the former Soviet countries and USA. I doubt it.
Here is a link: http://rortybomb.wordpress.com/2010/09/29/pew-economic-mobility-project-incarcerations-effects-on-economic-mobility/