BEIJING — In the end, the silences in the official “History of the Chinese Communist Party, 1949-1978,” speak louder than its nearly one million words.

Because the extraordinary thing about this two-volume work, published in January and widely discussed this month as the party celebrates its 90th anniversary, is that, while it contains some new details regarding controversial events in the first three decades of Communist rule, one gigantic subject is passed over in almost total silence: the deaths of tens of millions of people from political campaigns.

“Not less than 60 million,” said Frank Dikötter, a historian at the University of Hong Kong who is writing a book about the first years of the People’s Republic.

The new history matters to the party because it tells 82 million members what to believe, as the party seeks to enhance its credibility in an age when multiple information sources are available online....