The systematic, state-organized persecution and murder of six million Jews and millions of others by the Nazi regime and its collaborators between 1933 and 1945 — the most extensively documented genocide in history.
The Holocaust was not the product of ancient hatreds finally unleashed. It was the product of modern institutions — bureaucracies, railways, industrial chemistry, legal systems, professional armies — organized by a 20th-century state and implemented by ordinary people making incremental choices. That is what makes it so difficult to understand, and so impossible to dismiss as an aberration.