In 1940 the Japanese government, after negotiating a treaty of friendship with Thailand, sought special concessions in Indochina from the French colonial authorities. The Vichy administration in Hanoi, under pressure from the German government, signed an agreement with Tokyo that permitted the movement of Japanese troops through the transportation hubs of Indochina.

Thailand subsequently sought to take advantage of both its friendship with Tokyo and French military weakness in the region by launching an invasion of Cambodia's western provinces. Although the French suffered a series of land defeats in the skirmishes that followed, a unique twist in the confrontation came from a naval battle that ensued near the Thai island of Ko Chang. A small French naval force intercepted a Thai battle fleet, en route to attack Saigon, and sank two battleships and other light craft. The Japanese then intervened and arranged a treaty, signed in Tokyo in March 1941, compelling the French to concede to Thailand the provinces of Batdambang, Siemreab, and parts of Kampong Thum and Stoeng Treng. Cambodia thus lost one-third of its territory and nearly half a million citizens.

The Japanese, while leaving the Vichy colonial government nominally in charge throughout Indochina, established in Cambodia a garrison that numbered 8,000 troops by August 1941. Preservation of order on a day-to-day basis, however, continued to be the responsibility of the colonial authorities, who were permitted to retain the constabulary and the light infantry battalion. These forces were sufficient to quell the first stirrings of nationalistic unrest in 1941 and in 1942.

Anti-French agitation assumed a more overt form, in July 1942, when early nationalist leaders Pach Chhoeun and Son Ngoc Thanh organized a demonstration in Phnom Penh over an obscure incident involving Cambodian military personnel. In this occurrence, a monk named Hem Chieu attempted to subvert some Khmer military personnel by involving them in vague coup plotting against the colonial administration. The plot was discovered, and the monk was arrested Chhoeun and Thanh, believing they had tacit Japanese support, staged a march on the French residency by some 2,000 people, many of them monks. The repressive reaction by the colonial authorities resulted in many injuries and in mass arrests. Although the Japanese failed to support Thanh as he had expected, they spirited him away to Japan, where he was trained for the next three years and was commissioned a captain in the Japanese army. Chhoeun was arrested and sentenced to life imprisonment.

On March 9, 1945, Japanese forces in Indochina, including those in Cambodia, overthrew the French colonial administration and, in a bid to revive the flagging support of local populations for Tokyo's war effort, they encouraged indigenous rulers to proclaim independence (see The Emergence of Nationalism , ch. 1). During this period of Japanese-sponsored independence, the fate of the constabulary and of the light infantry battalion rec1a remained uncertain. The battalion apparently was demobilized for the most part, while the constabulary remained in place but was reduced to ineffectuality. Presumably both forces were leaderless because their French officers were interned by the Japanese for the remainder of the war.

Tokyo, however, did not plan to leave the Indochinese countries without a military force following the March 9 coup. Plans had been prepared for the creation of 5 volunteer units of 1,000 troops each. There was no thought that such a native force would fight alongside Japanese troops, but rather that it would be used to preserve public order and internal security. It was intended that recruitment of indigenous personnel for the volunteer units would be through physical and written exams. Before the plan could be implemented in Cambodia, however, the war ended, and the concept died without further action.

The conclusion of World War II caused considerable turmoil in Cambodia: a defeated Japanese military contingent waited to be disarmed and repatriated French nationals newly released from internment sought to resume their prewar existence diverse Allied military units returned to Phnom Penh to reimpose a colonial administration. In the countryside there were two sources of unrest. On the western fringes of the country, the Khmer Issarak (see Appendix B), nationalist insurgents with Thai backing, declared their opposition to a French return to power in Cambodia, proclaimed a government-in-exile, and established a base in Batdambang Province (see fig. 1). On the eastern frontier, the Vietnamese communist forces, or Viet Minh (see Appendix B) infiltrated the Cambodian border provinces, organized a "Khmer People's Liberation Army" (not to be confused with the later Cambodian force, the Kampuchean (or Khmer) People's National Liberation Armed Forces [KPNLAF--see Appendix B], which is sometimes called the Khmer People's National Liberation Army), and began seeking a united front with the Khmer Issarak.

Data as of December 1987