The Addis Ababa Massacre: Italy’s National Shame. By Ian Campbell. Hurst; 478 pages; £30. To be published in America by Oxford University Press in August.

NEAR the village of Affile, on a picturesque hillside east of Rome, stands a monument, unveiled in 2012 and built with public funds, to Rodolfo Graziani, one of Mussolini’s most brilliant generals. He was a key figure in Italy’s brutal campaigns in Africa in the decade before the second world war.

Inside a roundabout in Addis Ababa lies another monument. This giant obelisk, perhaps the Ethiopian capital’s finest piece of public art, was donated by Josip Tito, then president of Yugoslavia, in 1955. Six bronze reliefs depict a massacre, the worst in Ethiopian history, carried out by Italian forces during the occupation of 1936-41 while Graziani was viceroy of Italy’s new colony. According to the Ethiopian government, some 30,000 Ethiopians died during the campaign of terror in February 1937.

Official Italian estimates usually number between 600 and 2,000, but they are certainly much too low. The most plausible figure, argues Ian Campbell in the first comprehensive account of the massacre, may be 20,000. In Italy Graziani’s great crime is seen as little more than a typical European colonial atrocity—no worse than the British at Amritsar, for instance, where 1,000 people (according to India’s count) were slaughtered in 1919.

But, as Mr Campbell’s meticulous work makes plain, this was no typical colonial atrocity. After a failed attempt on Graziani’s life, the Italians’ bloody revenge lasted three days. Led by the local “Blackshirts”—Mussolini’s paramilitaries, officially granted carta bianca—regular soldiers, carabinieri and perhaps more than half of Addis Ababa’s Italian civilians took part. In this ghoulish massacre, witnesses reported crushed babies, disembowelled pregnant women and the burning of entire families.

Mr Campbell argues that this was a methodical effort to wipe out Ethiopian resistance to Italian rule, more like later Nazi war crimes than earlier colonial massacres. He charges both Graziani and the local Fascist Party leader, Guido Cortese, with personal responsibility. Though unconscious when the killing began, Graziani took control of the subsequent reprisal executions, aimed in particular at eliminating the Ethiopian nobility and intelligentsia.

Graziani was never prosecuted for crimes in Africa, though he was convicted for collaboration with the Nazis and briefly imprisoned. Britain, wary of setting awkward precedents, played an outsized role in sheltering Italians with blood on their hands. Mr Campbell cites a telegram written by Winston Churchill to his ambassador in Rome in 1944, instructing him to protect Marshal Badoglio, Italian commander of the Ethiopian northern front, who used poison gas, and is considered the top war criminal by Ethiopia.

Italy was never forced to reckon with Fascism as Germany was with Nazism. Few post-war Italian historians ever tackled the massacre. Those that did were often denounced as unpatriotic. Angelo Del Boca, writing in the 1960s, was accused by the Italian army of being a “liar” for his research on Graziani’s crimes. When “Lion of the Desert”—a film depicting his actions in Libya—was released in 1981, it was soon banned, for damaging the honour of the Italian army. To this day Italian schoolchildren are not taught about the Addis Ababa massacre. Graziani is little known; his sins even less so. Mr Campbell’s book will be welcomed by the Ethiopian government, which has long argued that its citizens deserve an apology.