Who's reading the new edition of Mein Kampf? Not who Germans feared.

When the copyright expired on Adolf Hitler’s Mein Kampf at the end of 2015 – opening shelf space for a new critical edition – some Germans worried it would become a hit at precisely the worst time. Some 1 million refugees had entered Germany, stirring anti-immigrant sentiment that has buoyed the once-taboo far-right.

This week, the publisher of “Hitler, Mein Kampf: A Critical Edition” seemed to confirm moderates' worst fears, announcing that the two-volume annotated edition was a non-fiction best-seller in Germany last year, just as Hitler’s original was between the two world wars.

But the demand is being driven not by neo-Nazis, the publisher says – rather, by teachers, libraries, history buffs, and those yearning to understanding the parallels between the populism of now and then.

Sven Felix Kellerhoff, a German author and journalist, wrote a book called “Mein Kampf," in 2015, tracing the history of a tome whose title is well-known but whose content is not. He says his book and the new critical edition help destroy the enigma surrounding a treatise that is badly written and poorly conceptualized but laid the groundwork for World War II. The original, which outlines Hitler’s hatred of Jews and ultimately led to the Holocaust, was banned at the end of that devastating conflict. But prohibition in more recent times has tended to shroud it in mystery, he says.

“Mein Kampf was dangerous only as a myth, as a rumor, as a so-called ‘banned book.’ Now, with the very good scientific edition and maybe a little bit with my own book, this myth is destroyed,” Mr. Kellerhoff says.

The Munich-based Institute for Contemporary History (IfZ), which published the 1,948-page work, initially planned to print 4,000 copies, and at the time acknowledged the sensitivity around its publication for the first time since 1945. Tuesday it announced it has since sold 85,000 copies and is releasing its sixth edition at the end of January.

"It turned out that the fear the publication would promote Hitler's ideology or even make it socially acceptable and give neo-Nazis a new propaganda platform was totally unfounded," IfZ director Andreas Wirsching said in a statement. “On the contrary, the discussion about Hitler's world view and how to deal with his propaganda offered the opportunity to look at the disastrous roots and consequences at a time when authoritarian political ideas and right-wing slogans are again gaining followers.”

That sentiment speaks to an entire cultural rethink of remnants of the Reich. While reporting a Christian Science Monitor magazine story last year in Nuremberg, which was contemplating how to preserve the Nazi Rally Grounds, I met Cornelia Kirchner-Feyerabend, a high school history teacher. That day, she was thumbing through an antique edition of an original “Mein Kampf” that one of her students brought in. It was his great-uncle’s, who received it as a wedding gift from his city's mayor.

She said her own high school teacher would not have dared bring the book into his classroom. At that time, Hitler’s text was treated as something to be locked in the “poison cabinet.” She couldn’t wait to get her hands on the new critical edition, which had sold out quickly.

The book's debut last year happened to fall just after mass sexual assaults during Cologne’s New Year’s Eve celebration, which was blamed mainly on men of North African and Middle Eastern descent and inflamed anti-refugee sentiment.

At a bookstore at the city’s train station, one customer told me his uncle had asked him to buy him a copy. He refused on the grounds that he wanted nothing to do with Hitler, “that psychopath.”

Another customer admitted he’d be self-conscious about flipping through pages in public because he wouldn’t want anyone to think it was out of contempt for the refugees who have come to Germany. But he planned to buy “Hitler, Mein Kampf: A Critical Edition" because he saw an opportunity to glean new insights. “You get a chance to learn more about that history, to understand it’s not the truth,” he said.

Mr. Kellerhoff says when he takes his own book to German schools, he always gets the same response: a recognition by the students that Mein Kampf offers only simplistic answers to difficult problems.

”It’s like the refugees. Of course you can say all refugees should get out of Europe," he says. "But that is not possible. It’s a simple answer. … This thinking leads to catastrophe.”