When I was in graduate school I read many books that shaped my understanding of historical events, but few did so as profoundly as Christopher Browning's Ordinary Men. By using a battalion of reservists as a case study, Browning showed the process by which men not motivated by ideology or hatred or careerism became participants, even enthusiastic ones, in the execution and deportation of thousands of Jews during the Holocaust.
Though Browning referenced the experiments undertaken by Stanley Milgram and Philip Zimbardo to explain the psychology of their participation, it's also easy to see the germ of his argument in Hannah Arendt's famous book. For while he was a member of the Nazi Party and a member of its security apparatus, Arendt argues that Adolf Eichmann was less a committed anti-Semite than someone who craved the structure of being part of a larger organization that would give him purpose. Many people have taken this as something of an exoneration of what Eichmann did in his role organizing the deportation of Jewish people, yet this is a misreading of Arendt's analysis, as she makes it clear that Eichmann took pride in his accomplishments and she dismantles his efforts to hide behind the governmental hierarchy. What makes her book so powerful is the sense she conveys of Eichmann, who justified to himself the facilitation of the murder of millions as part of a greater enterprise of which he was proud to serve. Is it this sense of mission devoid of ideology which is at the heart of her assertion of Eichmann's banality.
In the decades since Arendt's book has been published some writers have criticized her for minimizing Eichmann's ideological devotion to Nazism. And while works such as Bettina Stangneth's Eichmann Before Jerusalem do offer important qualifications of Arendt's interpretation of her subject, her book remains essential reading for anyone seeking to understand the motivations of the men and women who carried out the murder of millions of people. For while racism was an undoubted motivation for some, for many others it was a matter of duty, an enjoyment of the power held, or simply a sense of going along with the group. In many ways that was far more horrifying than the anti-Semitism that sparked the Holocaust in the first place: the people who don't just do nothing in the face of evil, but who enable it with their indifferent participation.