HONG KONG — The worst catastrophe in China’s history, and one of the worst anywhere, was the Great Famine of 1958 to 1962, and to this day the ruling Communist Party has not fully acknowledged the degree to which it was a direct result of the forcible herding of villagers into communes under the “Great Leap Forward” that Mao Zedong launched in 1958.

To this day, the party attempts to cover up the disaster, usually by blaming the weather. Yet detailed records of the horror exist in the party’s own national and local archives.

Access to these files would have been unimaginable even 10 years ago, but a quiet revolution has been taking place over the past few years as vast troves of documents have gradually been declassified. While the most sensitive information still remains locked up, researchers are being allowed for the first time to rummage through the dark night of the Maoist era.

From 2005 to 2009, I examined hundreds of documents all over China, traveling from subtropical Guangdong to arid Gansu Province near the deserts of Inner Mongolia.