"Perpetrators of Genocide: An Explanatory Model of Extraordinary Human Evil", by James Waller:
The twentieth century, the "Age of Genocide", moved from the near-complete annihilation of the Hereros by the Germans in South-West Africa in 1904; to the brutal assault of the Armenian population by the Turks between 1915 and 1923; to the implementation of a Soviet man-made famine in the Ukraine in 1932-1933 that left several million peasants starving to death; to the Soviet deportation of entire nations; to the extermination of two-thirds of Europe’s Jews during the Holocaust of 1939-1945; to the massacre of approximately half a million people in Indonesia during 1965-1966; to mass killings and genocide in Bangladesh (1971), Burundi (1972), Cambodia (1975-1979), East Timor (1975-1979) and Rwanda (1994); and, finally, to the perpetual human crisis that continues to rage in the former Yugoslavia.

Insightful study featuring an Explanatory Model of Extraordinary Human Evil and namedropping works ranging from Theodor Adorno's The Authoritarian Personality to Reinhold Niebuhr's Moral Man and Immoral Society, from Daniel Jonah Goldhagen's Hitler’s Willing Executioners: Ordinary Germans and the Holocaust to Hannah Arendt's Eichmann in Jerusalem: A Report on the Banality of Evil.

A review to counteract and dismiss James Waller's assertions, amongst other assertions including Susan Neiman and the Lisbon earthquake (cf. Nepenthe's post titled Evil), can be found in the Books & Culture section of Christianity Today.
In fact, since the Holocaust features so prominently in every study of evil - though we know it's been so very advertised, as opposed to the seventy years of terror and famine under Stalin's rule - here is a Bookstore on the Holocaust.

[To think that a friend found this by searching for the word 'extraordinary'... Thanx :-)]