Every Jew knows the story. The evil tsarist authorities ride into the Shtetl. They demand a levy of young men for the army. Mothers’ weep. Fathers’ sigh. The community mourns the loss of its young. It’s a good story, and some of it’s even true.

Scholars argue about whether the Holocaust was unprecedented. It’s a difficult question. On the one hand, slaughters litter the pages of history. On the other hand, none of them seem quite as calculated, systematic and horribly efficient as the Nazi mu...