Is it really only a 2x factor? I'd have to dig up some numbers, but my impression was more like a 5-10x differential, even going by actual sentences, not maximums. For example, 98% of sentences in Denmark are 24 months or less; it's very difficult for the prosecution to get a multi-year sentence except in exceptional circumstances (serious violent crimes, career criminals on their 3rd or 4th trial, etc.). My impression (possibly incorrect?) is that the U.S. much more frequently makes use of severe sentences in the 5+ year range, even for nonviolent property crimes, or drug-possession offenses.
I think I recall a study arguing that the massive disparity in sentence lengths, rather than rate of arrest/conviction, was the main contributor to the U.S.'s very large prison population. I.e. Europeans also arrest and convict people, but they don't keep them in prison for multi-year lengths nearly as often.
The U.S. is generally less than 2x relative to Australia, 2-3x relative to the U.K., and 3-5x relative to Finland. The sentences for assaults show the most differential, I'd imagine because of very strict sentencing for sexual assaults.
I think the averages skew higher in the U.S. than typical sentences than it does in other countries. Initiatives like California's "three strikes law",[1] that result in life sentences for three potentially non-violent felonies dramatically skew up the averages in the U.S. I don't think any of the major European countries have anything comparable. If you took out the ridiculous sentences handed down as a result of those laws, I think the differential would be much less.
I think I recall a study arguing that the massive disparity in sentence lengths, rather than rate of arrest/conviction, was the main contributor to the U.S.'s very large prison population. I.e. Europeans also arrest and convict people, but they don't keep them in prison for multi-year lengths nearly as often.