But incarceration rate per population doesn't tell you if the population is being over-incarcerated unless you know the crimes-worthy-of-incarceration rate. If America's rate of crime-worthy-of-incarceration is several times the European, then it's perfectly natural the US has a several-times-higher incarceration rate.

Now, there are all sorts of difficulties in calculating such a rate. But it doesn't seem too unreasonable to guess that, however it's calculated, the general rate of crime-worthy-of-incarceration would correlate with the homicide rate. So, let's use the homicide rate as a normalizer. How many incarcerated persons does a country have per annual intentional homicide? Using the Wikipedia numbers for prisoners and annual intentional homicides, we get:

Australia: 121

Belgium: 68

Bulgaria: 73

Canada: 74

Croatia: 90

Czech Republic: 163

Denmark: 91

Estonia: 46

Finland: 36

France: 103

Germany: 98

Greece: 71

Hungary: 142

Iceland: 157

Ireland: 74

Israel: 138

Italy: 111

Japan: 170

Latvia: 56

Lithuania: 48

Luxembourg: 164

Netherlands: 91

New Zealand: 203

Norway: 33

Poland: 175

Portugal: 115

Romania: 96

Slovakia: 134

Slovenia: 94

South Korea: 109

Spain: 180

Sweden: 86

Switzerland: 145

Taiwan: 91

UK: 147

US: 147

Thus, the US incarceration rate differential is within the normal variation seen in developed countries, after you account for the fact that the US has a lot more violent crime than other developed countries (as seen in its much higher homicide rate).