The Kingdom of Kampuchea (Khmer: ព្រះរាជាណាចក្រកម្ពុជា; Japanese: カンボジア王国) was a short-lived puppet state of Imperial Japan, which existed from 13 March 1945 to 16 October 1945.

The Japanese hoped to revive the flagging support of local populations for Tokyo's war effort by encouraging indigenous rulers to proclaim independence.

[2] Sihanouk's decree did away with previous French-Cambodian treaties and he pledged his newly independent country's cooperation and alliance with Japan.

However, Son Ngoc Thanh, another of the men behind the Khmer-language newspaper Nagara Vatta who had fled to Japan following the 1942 anti-French demonstrations, had returned in April 1945 to serve as foreign minister.

Some of his supporters went underground and escaped to Thai-controlled northwestern Cambodia, where they were eventually to join forces in a pro-independence group, the Khmer Issarak.