Short answers, pulled from the story.
The Hundred Regiments Offensive ran from the 20th of August 1940 to the 24th of January 1941. It was launched by the Eighth Route Army of the Chinese Communist Party against Japanese forces in North China.
The offensive ultimately involved 105 regiments and approximately 200,000 troops. The original plan called for only 22 regiments, but the number expanded rapidly as additional units joined the campaign.
The primary objective was to destroy the Shijiazhuang-Taiyuan railway, known as the Zheng-Tai Line, which was a key element of the Japanese "prison cage policy" in North China. The campaign also aimed to attack fortified Japanese strongholds and disrupt transportation corridors across the region.
The offensive was ordered by Zhu De, Commander-in-Chief of the Eighth Route Army, and directed in the field by Peng Dehuai, his deputy. Zuo Quan, Deputy Chief of Staff, co-signed the original Preliminary Battle Order issued on the 22nd of July 1940.
Japanese military records vary from Chinese accounts. Chinese reports claimed between roughly 12,000 and 20,000 Japanese killed or wounded, while Japanese records document 276 killed for the 4th Independent Mixed Brigade and 133 killed for the 2nd Independent Mixed Brigade. A western source estimated approximately 20,900 total Japanese casualties.
Peng Dehuai and Mao Zedong had disagreed since at least 1937 about how directly to engage Japanese forces. During the Cultural Revolution, a Red Guard group accused Peng of launching the offensive without Mao's authorization. Peng was prosecuted partly on the basis of these charges, though subsequent investigation and the post-Cultural Revolution consensus supported the campaign's legitimacy.