Nearly six decades after Josef Stalin's death, a debate has erupted in Germany on how to evaluate the Russian dictator's regime. It's been triggered by a newly released book by a high-profile Eastern European historian.

In his book, Jörg Baberowski delivers plenty of material for debate about the controversial Russian ruler Stalin. But the historian himself is uncompromising in his analysis. The ruler, he argues, was a passionate and ruthless psychopath, a despot who killed according to quotas, sparing no one, who sowed fear, horror and mistrust in his immediate surroundings and subjected an entire society to a culture of destruction and terror.

In his evocative book, Baberowski makes a case for this thesis on nearly 600 pages, quoting a wide range of sources. "I have not written a book about the Soviet Union or about Stalinism but rather about excessive force and what it does to people," said the author and professor of Eastern European history at Humboldt University in Berlin in one of his many packed lectures....