It is less than 30 years ago that the 20th-century's bloodiest dictator was approaching death, his country still dirt poor, his vision in ruins, with tens of millions of his fellow citizens dead at his hands. Today, that same country has enjoyed three decades of the most unparalleled economic growth. Mao's death has proved the trigger for an extraordinary economic renaissance. Nobody can disagree that he was a cruel and authoritarian despot who murdered millions; even his successor, Deng Xiaoping, pronounced that he was at least 30 per cent wrong and guilty of 'excesses'.  The open question is how much more wrong he was than the official assessment, how much of his legacy still informs the communist leadership and whether his long shadow and his thinking is any guide to what China might do in the future. If you think he was 100 per cent wrong, you must worry; China's Communist party has an evil DNA in its genes that will one day provoke war and mayhem with global implications. Agree with Deng and you might be more hopeful.  A new book, Mao: The Unknown Story (Jonathan Cape), places Mao unambiguously in the 100 per cent wrong category. Jung Chang, author of the compelling Wild Swans, the story of today's China through the pained eyes of three generations of women, and her husband, Jon Halliday, have used 10 years of research to indict comprehensively Mao's cynical lust for power and careless disregard for humanity. Whether it's the news that Mao never actually marched in long stretches of the Long March but was, instead, carried in a bamboo litter he designed himself, or of the scale of his purges and executions, this is a catalogue of disclosures that overturns almost all our received wisdom. The impact will be substantial.  It's an impressive achievement, but the book's unyielding view that there is not one even unintended benefit from his legacy leaves me uneasy. Mao is presented as an evil genius visited upon an innocent China courtesy of communist ideology which he cynically manipulated, who delivered nothing but murder and economic disaster.  It is blood lust and quest for world domination, for example, that drove Mao to consecrate the overwhelming share of China's scarce resources to the military in the first five-year plan; the drive to build dams and irrigation systems was carried out irrespective of the lives either of the builders or those later drowned by their collapse. When he saw violence at close quarters, he acknowledged it induced a kind of ecstasy.  And any idea that Mao was a great military strategist is dashed; even his victories are revealed as either disguised fiascos or the results of political fixes. Essentially, he led the communists to power by betraying efforts to find a common front against the invading Japanese, which he openly acknowledged, while carefully courting Moscow.  We are spared no detail of Mao's weaknesses - his failure to take a bath for 25 years, his 50-odd personal estates and his habit of having fresh fish delicacies from Wuhan carried 1,000 kilometres for his epicurean delight. I agree; guilty on all charges.  But Mao didn't come from nowhere. If you don't know about the century of China's humiliation, the complete bankruptcy of the Qing dynasty as it imploded in 1911 and the subsequent ungovernability of China and the apparent hopelessness of any project that might even half successfully modernise it, then it's hard to understand how it could be that Mao and Chinese communism would have any appeal. You will learn little of such context in this biography.  There is no country in modern times that has ever suffered so many defeats at so many hands as China did between 1842 and 1911; the British, the French, the Russians and the Japanese all easily disposed of Chinese armies and fleets. In 1898, the Western powers, including Germany, took great chunks of China and Chinese ports to administer for their own benefit. China was so weak that there was no point in spending money colonising it; foreign powers could get all they wanted by expending much less effort.  For the Chinese, their weakness was a complete bouleversement of their universe, and the contemptuously low status in which self-consciously racist foreigners held them (little more than animals) poured further salt in a gaping and humiliating wound. The system that had provided them with order for millenniums, granaries for famine, law, canals, agricultural prosperity and a sophisticated Confucian bureaucracy - and which presented the astounded Marco Polo as a civilisation more advanced, more peaceful and evidently superior to the never-ending conflict and barbarism of Europe - could neither rejuvenate itself from within nor begin to match the overwhelming achievements of the West.  How was this vast country, now collapsing into a myriad of local wars with peace provided by rapacious local warlords routinely deploying torture, to be governed? How was it to be industrialised? How could it defend itself against further despoilment by foreigners?  Communism, paradoxically building on the Confucianism it deplored, provided an answer, the reason it drew so many adherents. The strategy for modernisation - raising agricultural productivity by trial-and-error attempts at combining collectivisation with respect for village structures while building up industry on an equally decentralised basis - was very different from Stalin's centralised Sovietisation, despite the surface parallels.  It was more closely modelled on the imperial system than either critic or supporter ever concedes. And when Mao died, the second paradox is that the decentralisation and pragmatism he fostered, notwithstanding mad forays such as the campaign to kill sparrows, allowed Deng, the architect of today's China, quickly to put in place policies that would drive the astonishing economic turnround.   As for Mao's preoccupation with military spending, I submit that any new government in the 1950s would have placed an overwheening priority on defence, given China's history.  While the Great Leap Forward and the disaster of the Cultural Revolution are famed exercises in futility, personal delusion and inhumanity, brilliantly documented by Chang and Halliday, don't forget that between one and the other Chinese growth averaged 15 per cent per annum, never achieved before in a single year in China's long history.  China's vast rural hinterland was becoming, via the conception of village enterprise, the springboard for today's economic growth.  It would take Deng's opening up to trade and investment along the coast, and the reintroduction of capitalism, to make the most of the opportunity. But a Stalinistic communism would never have created the chance in the first place, as today's Russia bears grim witness.  Mao is now revealed as more of a monster than we ever guessed, thanks to Chang and Halliday. But even monsters can create good they may never have self-consciously aimed for or wanted.  History is the story of contradictions and unintended consequences. This book - and our understanding of China - would have been stronger still had it acknowledged them.