Whenever the history of twentieth-century communism is discussed, it will not be long before you find a particular figure cited with absolute certainty. Writing in the Wall Street Journal on the centenary of the October Revolution, David Satter informed its readers that communism was “the greatest catastrophe in human history,” having been responsible for one hundred million deaths.

The British Conservative politician Daniel Hannan had a similar message as he prepared for “the most monstrous of centenaries.” According to Hannan, communism was far worse than slavery or Nazism: “The Atlantic slave trade killed perhaps 10 million people, the Nazis 17 million — but the Communists killed 100 million.” The Victims of Communism Memorial Foundation, which runs a museum in Washington, carries the following message on its website: “Communism Killed Over 100 Million: We’re telling their stories.”

These claims ultimately rest upon a highly influential collection of essays titled The Black Book of Communism that was put together under the direction of French academic Stéphane Courtois. Originally published in French, the Black Book has been translated into multiple languages. Yet far from representing the established consensus among historians, the claims that Courtois made in the book’s introduction were not even accepted by all of his own contributors, some of whom were harshly critical of their editor after seeing the final product.