You’re comparing Norway’s 2 year recidivism Reconviction rate with the US’s 2 year Reimprisonment rate. The US’s 2 year Reconviction rate is 36%.

Even if those are the correct numbers to compare (which the other reply to you is questioning), the US number is 45% higher than Norway's which is still quite significant. Using the 36% rate from the other reply to you, the US rate is instead 80% higher than Norway's.

What I find striking are the reported recidivism rates of Sweden and Norway: 43% vs. 20% after 2 years. Sure, Norway is richer and socially/ethnically more homogeneous, but can this be the whole explanation for this extreme difference, considering the two countries are otherwise very similar?

Well Norway is a fraction the size of the US in population.

I would imagine that wealth, cultural homogeneity, and a very small population accounts for at least 80% of the explanation. So not the “whole” explanation, but the critical mass of why it works, sure.

It’s questionable to assume that Norway’s system could scale up by a factor of even 3x, let alone something sixty times the size. I’d be interested if it could produce results in a country like Spain or France with 50m people before calling on the US to simply do what Norway does but with 350m people.

Sure, but my question is about the difference between Norway and Sweden. Sweden has (merely) twice the population size of Norway, is culturally similar, highly developed, has a similar political system etc, but still seems to fair far worse.

Why not implement it at a state level then? Many states in the US have a similar population to Norway.