BEIJING (NYTIMES) - It seemed that China's censors had finally muzzled Yang Jisheng, the famed chronicler of the Mao era.

Last year, he had finished writing a widely anticipated history of the Cultural Revolution. But officials warned him against publishing it and barred him from traveling to the United States, he has said, and he stayed muted through the 50th anniversary of the start of that bloody upheaval.

Now Yang has broken that silence with the publication of his history of the Cultural Revolution, The World Turned Upside Down, a sequel to Tombstone, his landmark study of the famine spawned by Mao's policies in the late 1950s.

The 1,151-page book is the latest shot fired in China's war over remembering, or forgetting, the dark side of its Communist past, a struggle that has widened under the hard-line president, Xi Jinping.

"I wrote this book to expose lies and restore the truth," Yang writes in the book, which has been quietly published in Hong Kong, beyond the direct reach of Chinese censors.

"This is an area that is extremely complicated and risky, but as soon as I entered it, I was filled with passion."

Since Xi took power in 2012, Communist Party authorities have denounced historians who question the party's lionisation of its past and exhume grim events like the Cultural Revolution, which Mao started in 1966, opening a decade of purges and bloodshed.

Tens of millions were persecuted and perhaps 1 million or more people were killed in that convulsive time. But officials say dwelling on such events is subversive "historical nihilism" aimed at corroding the party's authority.

In a sign of how Chinese politics has chilled, Yang has said little publicly about the book.

"Since the book was published, I've been told not to discuss it with foreign media," he said in a brief telephone conversation.

He would not say whether he had authorised "The World Turned Upside Down" to be published in Hong Kong.

"There's quite a lot of pressure," Yang said. "I just wanted to restore this big story and the facts behind it, to recover the history."

Yang, 76, was a university student in Beijing when the Cultural Revolution erupted. He threw himself into the early phase, when Mao unleashed student radicals to purge school leaders and Communist Party cadres.

Yang later worked as a journalist for Xinhua, the state news agency, watching as the fervour of the Cultural Revolution fractured into disarray and disillusionment. After a career in journalism, he turned to writing histories of contemporary China.

Up until several years ago, Chinese newspapers and magazines still published laudatory profiles of Yang. But now he is often denounced by Maoists emboldened by the hard-line pronouncements.

Party journals have attacked his conclusion that up to 36 million people died in a famine from 1958 caused by the Great Leap Forward, Mao's reckless attempt to leap into a communist utopia, which Yang chronicled in "Tombstone".

That book was published in Chinese in Hong Kong in 2008.

"Yang Jisheng is not a historian," an editorial in Global Times, an ardently pro-party Chinese newspaper, said last year.

"He leaves the impression that he's not interested in history, and virtually all his later works display strong political tendencies."

Last year, Yanhuang Chunqiu, a liberal-leaning Chinese history magazine where Yang was long a chief editor, was taken over by editors much more willing to toe the party line.

The changed atmosphere was also evident when a court in Beijing ordered a historian to apologise for questioning the party's heroic account of a 1941 battle in the war against Japan.

Last year, too, Chinese media mostly stayed silent about the 50th anniversary of the start of the Cultural Revolution. An exception was an editorial in the party's main newspaper, People's Daily, which urged citizens to look to the future.

"Chinese political culture, both past and present, insists that the legitimacy of rulers depends on an immaculate record of what they have done," said Perry Link, a professor at the University of California, Riverside, who has written widely about Chinese culture and politics.

"They're afraid that telling the truth about those events pulls the rug on their right to rule," he said.

"They want to be damn well sure that history stays inside its box."

Now that "The World Turned Upside Down" has appeared in stores, the next battle will be over whether people get to read it in China, where such books are banned.

The book began appearing in late December in Hong Kong, which keeps its own system of law, including much greater freedom than is found in mainland China.

That freedom has shrunk in recent years. Publishers there have been spooked by the 2015 abduction to China of five Hong Kong booksellers who peddled lurid, poorly sourced potboilers about China's leaders.

Even so, Hong Kong remains an enclave for books banned in mainland China. Piles of Yang's book in bookstores there suggest that mainland readers have been buying copies to sneak across the border, despite customs checks.

"Mr Yang's work is quite influential inside China," said Jian Guo, who with Stacy Mosher translated "Tombstone" into English and is translating "The World Turned Upside Down" with Mosher.

"Yes, some of his books, including 'Tombstone,' are banned on the mainland," Guo said. "But an electronic version of 'Tombstone' has been floating around since 2008, and an enormous amount of pirated copies has been distributed by small book vendors."

Guo, a professor at the University of Wisconsin-Whitewater, said the abridged translation of Yang's latest book would include about two-thirds of its original content.

"We expect to publish in 2019," Eric Chinski, editor-in-chief of Farrar, Straus and Giroux, said in an email. The company also published an abridged translation of "Tombstone" in 2012.

Yang's book is by no means the first history of the Cultural Revolution; several were published under official auspices in mainland China in earlier decades as the Chinese government tried to confront the ordeal of the era.

But in recent years, the party has become much more wary about allowing such research. Many younger people have only a sketchy idea of what happened when Mao started the Cultural Revolution to purge China of what he saw as threats to the purity and survival of his revolution.

Yang "wanted his readers to remember the tragedy of the past, whether it was the Great Famine or the Cultural Revolution, to reflect on it, to make sense of it, so that the tragedy would not repeat itself," said Guo, the translator.

"He considered this task of a conscientious rememberer to be all the more urgent now in the face of the officially enforced historical amnesia in China," Guo added.

Yang did not have extensive access to archives for his new book, as he did when he wrote "Tombstone".

Instead, he drew on hundreds of memoirs, histories and studies, many published in Hong Kong or available online, and there are fewer revelations than in his previous book.

As in other recent scholarship, Yang emphasises that much of the worst bloodshed came later in the Cultural Revolution, when Mao brought back the military and party apparatus to brutally enforce order.

"It's fair to say this is a work by an eminent journalist, rather than a product by an academic historian," said Warren Sun, a historian of the Chinese Communist Party at Monash University in Melbourne, Australia.

He said he had read some draft chapters of Yang's book, and found a few debatable claims.

But Yang "was working under very difficult conditions, and thus deserved great respect for his moral courage," Sun said.