After the Japanese first began their invasion in 1937, in each place the Japanese captured, a collaborationist army might be formed and given various names, such as "IJA Assistant Army", "Peace Preservation Corps" or "Police Garrisons" and so on. Later on, particularly under the Nanjing Nationalist Government they were re-organized in a system of Divisions, Corps and Armies.
During the Second Sino-Japanese War, the Japanese occupied area was in continuous need for troops to suppress revolts and to defend against sabotoge to the Japanese supply lines, which diverted much of Japan's regular army manpower. In order to solve its manpower shortage on the front line (especially after 1942), and maintain rule over already occupied areas in China, the Japanese began employing existing local soldiers and recruiting local people to be responsible for the occupied areas' public security. Accordingly the Japanese occupied area puppet regimes established the North China Zhi'an Army and Nanjing National Revolutionary Army. The various puppet regimes had nominal control over their own collaborationist army only, but Japanese military officers were authorized to command and transfer any collaborationist army units as they saw fit.
In 1938, the manpower in China's puppet armies was approximately 78,000 men, mostly the forces of the Provisional Government of China in North China. When Wang Jingwei established the Nanjing Nationalist Government after 1940, the numbers of the Chinese puppet army suddenly rose to 145,000 men. Most of these new forces were local puppet forces established in areas the Japanese occupied from 1937 in Eastern, Central and South China.
From 1942 to 1943 (probably as a result of the United States' entry into the war) the Imperial Japanese Army commanders permitted National Revolutionary Army commanders faced with a disadvantageous situation (often a result of being caught between the Communists and the Japanese army) to preserve their strength by temporarily surrendering to the Japanese, and then joining the Nanjing collaborationist army en mass. The result was the collaborationist army manpower started growing rapidly. According to the Chinese Communist Party statistics at the end of the Second Sino-Japanese War, about 62% of the men in the Chinese collaborationist army were originally with the National Revolutionary Army.
Furthermore, the worsening situation for Japan from 1943 onwards meant that the Nanjing collaborationist army was given a more substantial role in the defence of occupied China than the Japanese had initially envisaged, and this army was almost continuously employed against the Chinese communist New Fourth Army. In March 1943, a British intelligence report estimated the total number at 345,130 men.
Despite rapid growth in manpower and increased responsibility to support the Japanese, the collaborationist Chinese army suffered from very low morale because the general public in the occupied areas viewed them as Hanjian, or traitors to China, and many surrendered quickly to Chiang Kai-shek's forces during military engagements. Enemy prisoners of low rank were persuaded to renege and fight alongside anti-Japanese forces, but high-ranking prisoners were executed.
After the Japanese unconditional surrender in 1945, the Chinese military counted approximately 1.186 million collaborationist soldiers (excluding Manchukuo), but some estimates had the head count exceeding 2 million in total, which means the manpower of the collaborationist army surpassed that of the invading Japanese army (the only time this was seen in any country during World War II).