It is wrong to say that “the British Empire became truly popular only in the last half-century of its existence”. Except during a brief late-Victorian/Edwardian interlude, Britons remained “absent-minded imperialists”.Ferguson attributes 20th-century violence, including the hundred major conflicts between 1945 and 1983 which resulted in 19 million deaths, to three main factors. Countries with the largest empires were not necessarily “best able to withstand the Depression” – France, with colonial possessions second only to Britain’s, suffered an “economic Sedan”. Ferguson might have noted, for comparison, that in 1800 two tons of Caribbean sugar cost the life of one slave.He is surprisingly fallible, though, for someone who made his reputation as an economic historian. German workers did not become much “better off” between 1933 and 1939, as Richard Evans shows. General Motors provided a tenth of all US war production and Ford manufactured more military equipment than Italy.

For every additional 19 tons of steel produced during the Stalinist period, one Soviet citizen perished. During the Second World War four Western soldiers were captured for every one killed in the Pacific; one Japanese was captured to 40 killed. During a conventional bombing raid on 9 March 1945 almost 100,000 citizens of Tokyo were, in General Curtis LeMay’s words, “scorched and boiled and baked to death”. After all, as Stalin discovered, the F?r could not be trusted.Ferguson’s statistics are copious and telling. Unlike other right-wing historians, he censures Chamberlain’s attempts to appease Hitler. Ferguson maintains convincingly that Britain and France should have gone to war in 1938, when Germany was weak and Russia might have joined Czechoslovakia to form a strong eastern front. Similarly, he dismisses the notion that Churchill might have saved the British Empire by negotiating a separate peace with Hitler.

And his account of the internecine struggles between and among the great powers, mainly from the Boer War to the Korean War, reveals him at his best. His descriptions of atrocities will purge readers with pity and terror. He fixes on compelling details: no sooner had the Soviets seized Buchenwald than they used it to house their own prisoners.His judgements are usually incisive. Its further unique feature is that “the leaders of apparently civilised societies were able to unleash the most primitive instincts of their fellow citizens”.Here he is on more solid, if less original, ground. Instead of asserting that the last century saw the world’s bloodiest organised slaughter, he says “it witnessed a transformation in the kind of war waged by developed Western societies against one another”. The Second World War killed 59 million, 2.6 per cent of the world’s population; Genghis Khan, who killed 37 million, reduced it by a tenth.

He habitually butchered all the inhabitants of cities in his path – 1.6 million in Herat, about six times the number massacred during the Japanese “Rape of Nanking”.So in the last pages, Ferguson revises his grand claim. Pol Pot was responsible for two million deaths in Cambodia, but at least seven million died in King Leopold’s Belgian Congo. China’s Taiping rebellion alone annihilated more people than the First World War. Yet not only does he fail to substantiate it, but he adds a late appendix conceding that the last century was “not so uniquely bloody” after all.
As he shows in this inconsistent postscript, even with superior technology modern mass murderers could hardly match the achievements of barbarians, crusaders, colonialists and civil warriors. Most dramatically, Ferguson sets out a thesis: that the 20th century, the “age of hatred”, was “far more violent in relative as well as absolute terms than any previous era”. He makes eye-catching pronouncements but all too often they don’t bear scrutiny: he credits Mussolini, a weak dictator, with establishing “the first truly totalitarian regime”. He surveys immense swathes of territory, but his coverage is more episodic than panoramic.

This is the book of a six-part television series for Channel 4, and it has both virtues and vices of its genre. Niall Ferguson benefited from the research of many assistants, as he acknowledges; but apart from a short list of archives and a long bibliography, he provides no references. Williams’s book is a tribute not only to a remarkable couple, but to a people whose grace under pressure is hard to match anywhere in the world.Stephen Howe is a professor of history at Bristol University. Even if such an image serves only to offset the fear many feel for the rest of the continent, the Tswana have earned it. There is sadness that Seretse lived only to 59, but the wider story remains upbeat.Ruth remained beloved by and devoted to her adopted people. Botswana has prospered, with high rates of economic growth and one of Africa’s few genuine democracies. Alexander McCall Smith’s Botswanan detective stories are the latest indication that Botswanans are Britain’s favourite Africans.