When I studied in China in the early 1970s, at the height of Mao Zedong's personality cult, there were certain unquestioned truths about the Great Helmsman: that he was one of a handful of men who had founded the Chinese Communist Party in 1921; that he was a brilliant military strategist who had led the great breakout from encirclement by the Nationalist army, as well as the Long March to China's north-west, thus saving the Red Army for eventual victory in the civil war; that, unlike the Nationalist forces who thought only of defeating the communists, the Red Army was resolute in resisting the Japanese; that Mao was a great peasant leader who made a huge contribution to the theory of guerrilla war after his inspection of the peasants' revolt in Hunan Province in 1927; that the Red Army was a guer- rilla force which moved lightly among the people and was therefore much loved, in contrast to the Kuomintang armies, which were cruel and dishonest. Mao was the Chinese revolution - its Lenin, its Stalin and, for most of his benighted subjects, its Marx, too.
Today, the hysteria surrounding Mao has diminished. Young Chinese prefer sex, money, ambition and rock'n'roll to leadership cults. Mao has moved from being a living god to a dead one. He dangles from the rear-view mirrors of taxis, giving protection to the traveller; he sits in effigy in the temples that have been built to him in the Chinese countryside - a wrathful deity that must be appeased lest he turn on you. Yet the unquestioned truths survive, assiduously transmitted in what passes for history in the People's Republic, taught to generation after generation of schoolchildren. Adults in China may have their own private opinions about Mao, but so complete is the historical fraud perpetrated on the Chinese and the rest of the world that, until now, none but those who had personal access to the man could summon the ammunition with which to demolish the myth.
There is no longer any excuse: Jung Chang and Jon Halliday's meticulously researched biography explodes every one of these unquestioned truths and many more. The list is long and grim: Mao was a terrible military commander, and spent his time scheming how to appropriate the armies built up by others. Not only did he not found the Chinese Communist Party, but it was not even a Chinese idea - the Russians, as the old Soviet archives demonstrate, set it up. Not only did Mao not lead the Long March, but his colleagues hated him so much that they schemed desperately to leave him behind. The Red Army treated the local population and its own troops with savage cruelty, and rebellion and desertion were constant problems. Mao's chief discovery in Hunan in 1927 was a personal taste for cruelty, and the belief - one that he never abandoned - in the efficacy of terror as an instrument of politics.
Yenan, destination of the Long March, is the locus of the party's myth of heroic endurance and sacrifice. But the truth, as Chang and Halliday reveal, is that Mao's Yenan was a place of hierarchy and privilege that swiftly disillusioned the young idealists who flocked there. In some ways, though, it remains the crucible of Maoism: it was there that Mao devised his first rectification project. He denounced Wang Shiwei, a young communist who had criticised the leadership's excessive privilege, as a Trotskyist. Wang spent his few remaining years in solitary confinement and was hacked to death at the age of 41. In April 1943, Mao arrested all those communists who had come from Nationalist-controlled areas on trumped-up charges of espionage. He transformed ordinary organisations into prisons and converted colleagues into jailers. He broke the trust between people and got them all informing on each other. He terrorised those closest to him. These were the hallmarks of the Maoist revolution.
Far from being hard-working, self- sacrificing and charismatic, Mao was lazy, lacking in charisma, personally debauched in his tastes and utterly ruthless. Even Zhou Enlai, his most loyal slave, did not escape: when, in the mid-1970s, Zhou was diagnosed with cancer Mao would not allow him an operation. He wanted Zhou to die first.
By Chang and Halliday's account, Mao would sacrifice anything and anyone for power. He abandoned the only woman he appears to have loved, his second wife, Yang Kaihui, and then attacked Changsha, the city where she was living along with their three young sons, without making any provision for her safety. (She was executed by the Nationalists in 1930.) He caused the death of his own brother in a power play, he set traps for his own soldiers, he framed and killed his own comrades-in-arms and, on the occasions when he was nudged out of power, he would stop at nothing to get back in. The authors estimate that the cost in Chinese lives was 70 million civilians, in peacetime.
This compendious biography, ten years in the research and writing, is an extra-ordinary exercise in iconoclasm that is likely to play its own part in changing history. The impact on Mao's reputation among his few remaining admirers in the west (step forward Edward Heath) will be profound. More interesting, however, is its likely effect in China.
The Chinese Communist Party's verdict on Mao was that he was a great leader who made "a few mistakes" - the cultural revolution being his last and most egregious. But the CCP still relies on the myth of Mao for its remaining shreds of historical legitimacy. Perhaps it is a symptom of the party's weakening grip on power that it was not able, finally, to prevent Chang and Halliday from tracking down informants, turning over archives and piecing together the truth. There may even be some in the party who recognise that China must confront the absurdities of the official account of the 20th century, and who hope that laying bare the truths that the CCP has never been able to face might be a step towards political reform.
China missed its moment to dispose of Mao in 1976: there was no Chinese Khrushchev. So completely had Mao appropriated the Chinese revolution, what would have been left if the party had denounced him? Instead, the CCP rushed to claim his mantle. When the destruction of Mao the god comes - as it surely must, the sooner for this book - his vengeance on the party might still be that of the wrathful deity. But when the Chinese people finally face the real history of the 20th century, there surely won't be a better place for them to start than this book.
Isabel Hilton's most recent book is The Search for the Panchen Lama (Penguin)