It was 20 years after I chose to become a historian that I first saw a photograph of the woman who made my career possible. In the small photograph that my doctoral supervisor, her son, showed me in his Warsaw apartment, Wanda J radiates self-possession, a quality that stood her in good stead during the Nazi occupation. She was a Jewish mother who protected herself and her two sons from the German campaign of mass murder that killed almost all of her fellow Warsaw Jews. When her family was summoned to the ghetto, she refused to go. She moved her children from place to place, relying upon the help of friends, acquaintances and strangers. When first the ghetto and then the rest of the city of Warsaw were burned to the ground, what counted, she thought, was the “faultless moral instinct” of the people who chose to help Jews.

Most of us would like to think that we possess a “moral instinct”. Perhaps we imagine that we would be rescuers in some future catastrophe. Yet if states were destroyed, […]