In the early stage of the First World War, the Union of South Africa invaded the neighbouring colony of German South West Africa at the request of the British War Cabinet. The assignment was to knock out a German coastal wireless station, but South Africa’s war leaders, Generals Louis Botha and Jan Smuts, got above themselves. Going the whole hog, they seized the territory from Berlin. In the peace negotiations which finally ended the Great War, Pretoria persuaded the victorious powers to allow it to keep the former enemy colony under its jurisdiction as a League of Nations mandate territory.

One of the arguments of the South African case was moral and humanitarian. The promise of a new colonial administration under the Union was that it would be enlightened and decent, far more humane than the former German overlords who had treated the Herero and Nama peoples with exceptional brutality. Granted, Botha and Smuts themselves were no milksops in their governing of Black people, but they had an irrefutable point. The Union’s 1919 Blue Book was probably not too far wrong in depicting German South West Africa as a kind of charnel house, stocked with corpses, chains, whips and execution yards.

As this sober and densely documented study reveals, Kaiser Wilhelm’s African colony of ‘South West’, resembled nothing so much as the Congo Free State, the gory Heart of darkness portrayed by the English novelist, Joseph Conrad. In the 1880s, Belgium’s King Leopold II had ravaged the Congo, flattening villages and hounding uprooted peasants into inhospitable forest and swamp land, where they were left to starve. Two decades later, the soldiers and bureaucrats of Kaiser Wilhelm II went a step further: between 1904 and 1909 they did their very best to plan and carry out the extermination of the Herero and Nama of present-day Namibia. It was undoubtedly the worst episode of colonial genocide in the 20th century.

What prompted it? In 1904, having grown increasingly discontented over the increasing land confiscations of German settlers greedy for lebensraum (living space), the pastoralist Herero and Nama peoples rose up against colonial domination. Their rebellions were scratchy affairs, neither properly coordinated nor effectively planned. And they went the way of other African peasant risings against colonial power, with rebels fated to be out-gunned, out-ridden and here, in sparsely populated South West Africa, also outnumbered. The cost to their German adversaries was trifling, but it did include the life of a farmer or two.

The ferocity of the imperial response was unimaginably disproportionate. Berlin embarked on a protracted war against not only resisting rebels but their societies. Conducted as a campaign of extermination, it has been estimated that over 60 000 Herero and 10 000 Nama were killed. The British–Nigerian and Danish authors of this well-researched book conclude that at least 80% of the Herero population were liquidated in what they call, quite aptly, The Kaiser’s holocaust. Unsurprisingly, that ill wind blew well for the lebensraum appetite of German colonists, as by 1908 the imperial German government was able to snatch many millions of acres of grazing land from wilting Herero and Nama inhabitants.

Of course, this was never (to make no bones about it) a routine colonial land war. It was a peculiarly ruthless and utterly relentless war for corpses. Olusoga and Erichsen document, in graphic detail, exactly what transpired in Kaiser Wilhelm II’s south-western Africa, a possession that he never even visited. A mountain of bodies piled up in the concentration camps into which people were herded after being run to ground in the wastelands of the Kalahari. The first and most notorious of these was established on Shark Island, off Luderitz, today a tourist resort known for shark-diving and seafront restaurants. Not all German bystanders were indifferent to what their countrymen were doing on Shark Island in the 1900s. With his stomach turned by what he was witnessing, in 1905 one distressed German missionary declared, ‘Luderitz lies heavy on my heart’.

A large chunk of The Kaiser’s holocaust is devoted to advancing its overriding argument about the colonial origins of later German genocide. Drawing on a wide range of evidence, these authors provide an assured account of the intellectual culture and political ideology of racial supremacy, rising like some pernicious yeast in late-19th and early-20th century Germany. Almost all of its settlers, soldiers and officials in South West Africa instinctively categorised Africans as subhuman if not animal, and were urged by the Kaiser personally not to allow themselves to be restrained in their actions by instincts of Christian morality or ethics. As a low species of life, these did not apply to the Herero and Nama. Wilhelm II rather fancied himself as a deep Teutonic thinker, visualising the German empire as a badge of superior racial nationhood, unlike the British, to whom empire was a grubby cash register. Unsurprisingly, he was fond of inviting both German and Dutch university professors to his country residence for tea and cake, over which to discuss the grand destiny of the German people, and the desirability of disposing of lesser peoples.

The demented logic of such visions led to the academies of Berlin. There, scientists who were increasingly obsessed with racial classification, phrenology and other measuring of racial types, were soon eyeing pictures of the bodies accumulating in Swakopmund and other places. Skeletons and severed heads preserved in alcohol were retrieved from concentration camps and their burial dumps and shipped back to university laboratories for evolutionary and other scientific study. Among many gruesome illustrations in this richly documented story is a standard soldiers’ postcard of the kind sent home to families from overseas service. It depicts a squad of smiling German soldiers busy packing Nama skulls into crates for shipment to Berlin, row by row.

The chilling shadow which that image throws is at the core of this grim story. For Olusoga and Erichsen, the roots of Holocaust Germany are to be found not in the carnage and trauma of the First World War, nor in the crises of German society produced by the burdensome terms of the Treaty of Versailles, but in its African colonial past. South West Africa was an early laboratory for genocide, just as civil war Spain was a practice ground for Luftwaffe aerial bombing techniques in the Second World War. The monstrous excesses of the territory’s military Commander-in-Chief, General Lothar von Trotha, in his open season of systematic killing and the deadly internment camps were the seed of Adolf Hitler’s Third Reich. In this view, Luderitz and Swakopmund were the Auschwitz and Dachau of their day. This argument may not be entirely convincing, given that it runs together two exceptionally distinct historical contexts. But it is certainly presented in a vivid, powerful and often compelling way, as the authors trace continuities in ideology, methods, functionaries and even dress styles between German colonial Namibia and Nazi Germany.

Whatever one’s view, this is a good and provocative perspective to consider. At the same time, the scholarly quality of The Kaiser’s holocaust is let down a little in a couple of respects. Although there is no shortage of fresh archival research, especially on the camps, the book is over-insistent on the novelty of its historical revelations. The terrible Namibia story has been turned over by a number of historians in specialised works in both German and English. Some of these, like those of Horst Drechsler, have been around for many years. Others, like that by Robert Gerwarth, are more recent and also more direct, as in his 2009 ‘Windhoek to Auschwitz’ essay in the European History Journal. This could all have done with some acknowledgement.

Then, too, there is the wider claim of historical amnesia over the fate of the Nama and Herero in this period. The Kaiser’s holocaust treats the Namibian genocide as a semi-subterranean episode, festering away in concealment, uncovered, papered over, reluctantly unearthed again but never fully confronted. To be fair, though, during the 2004–2005 centenary remembrance of the genocide, Germany and Namibia were both home to a rash of writing and public discussion of the significance of this traumatic moment in the history of the territory. For its part, the German government acknowledged its country’s bloodied hands and made a full apology.

So there is an air of looseness about some of this book’s more strident assertions. But, as a well-crafted example of accessible scholarship, it does an admirable job of laying bare what it was that weighed so heavily on the heart of at least one compassionate Luderitz missionary.