For decades, Yu Ruxin, a businessman turned independent historian, scoured used book stalls across China for frayed, yellowing documents about the Cultural Revolution, a decade of mass political upheaval unleashed by Mao Zedong.

The fruit of his long quest was published in Hong Kong this month, a 1,354-page history that sheds new light on the central role of the military during the Cultural Revolution. The People’s Liberation Army is widely known to have been called in to impose order, but Mr. Yu also documents in meticulous detail how the military was also involved in purges and political persecution.

“Through the Storm,” a two-volume Chinese-language book buttressed with 2,421 footnotes, stands out all the more these days, when the Chinese authorities are determined to erase the darkest chapters of the party’s history.

China’s leader, Xi Jinping, this month celebrated 100 years since the founding of the country’s Communist Party. The centenary has skipped over the political upheavals and mass suffering that characterized the party’s earlier decades in power.

Mr. Yu, 70, said he was not an opponent of the party, but that China should allow a candid accounting of the Cultural Revolution, when 1.6 million people were killed, by some experts’ estimates.

“We won’t be able to truly absorb the lessons of history, and history may just repeat itself,” Mr. Yu said in an interview from Hong Kong. “It couldn’t possibly be exactly like the Cultural Revolution, but something similar can’t be ruled out.”

Discussing such topics has become increasingly difficult in China in recent years. Historians and publishers have come under intense pressure to stick to the official line.