Grabowski concludes, from careful study of individual cases in one region, that Poles who murdered Jews were more likely to join the communist party that ruled Poland after the war. This confirms a suggestion that Gross made more than a decade ago: that people who collaborate with one occupation are likely to collaborate with the next. The frequency of double collaboration, a natural corollary of double occupation, forces us to restrain our tendency to explain violence by ideological conviction.

Timothy Snyder: Hitler’s Logical Holocaust