More than 1 million copies of the second volume of the "History of the Communist Party of China (CPC)" had been sold as of mid-May, just four months since the book was published after 16 years of painstaking editing, a senior official historian said Thursday.

Historians are now working on the third volume covering the post-1978 period when China embarked on the reform and opening up, said Li Zhongjie, deputy director of the Party History Research Center of the CPC Central Committee, at a press conference.

The second volume, which features major events of the CPC from 1949 to 1978, has dominated sales in major Beijing bookstores for weeks.

An entire chapter of the book is devoted to the Cultural Revolution (1966-1976), a time of turbulence when many Chinese suffered extraordinary hardship.

The first volume covers the years from 1921 through to 1949, a revolutionary period before the founding of New China.

According to historians, editing the second volume was difficult because it covers controversial periods, including the Great Leap Forward of 1958 and the Cultural Revolution.

Li said the publication not only acknowledges the Party's positive contributions, but also analyzes the causes of policy failures and the misjudgment of Party leaders.

"The CPC has learned from experiences and drawn lessons from its past," he said.

Li said efforts should be made to "put the most objective materials in historical records" after careful selection and soliciting opinion from various circles.

The CPC, the world's largest political party, will mark its 90th anniversary on July 1. It had 78 million members as of 2009.