Based on the assumption in recent research that Adolf Hitler only developed an eliminatory anti-Semitism with the announcement of the Versailles peace terms in 1919, the article examines the question of which psychological mechanisms were at work. It is a commonplace that the Treaty of Versailles was a “traumatic” experience for Hitler and many Germans. Was it also “traumatic” in the clinical sense of the term? If so, why and in what specific form did the historical event have a traumatizing effect? The phenomenon of Nachträglichkeit (deferred action) offers one possible explanation: Fears and feelings of guilt associated with the peace conditions and, above all, the “Schmachparagraphen” of the Treaty of Versailles reactivated traumas from early childhood, which only now experienced their full pathological effect. The approach pursued here offers a way out of the dilemma of determinism, as it emphasizes the fundamental openness of historical developments and analyses the interplay between individual psychopathology and key historical events.