On a freezing day in Paris in 1895, a captain of the French army was led into the courtyard of the École Militaire. Convicted on trumped-up charges of passing military secrets to the Germans, he was to undergo a ceremony of ritual humiliation. An officer tore the badges and stripes from his uniform and broke his sword. The crowd roared: “Judas! Traitor!” Alfred Dreyfus was a Jew. His ordeal at the military school was the beginning of a 12-year struggle that divided the country and unveiled the depths of French, and European, antisemitism: the Dreyfus affair. Watching the spectacle that...