The Japanese invasion of Southeast Asia between 1941 and 1942 had a limited effect on the existing situation in Indochina. During this period, the Japanese permitted the Vichy French to maintain control over daily administration. Sensing an opportunity, the Thai forces, aligned with the Japanese, launched incursions into Cambodia, aiming to reclaim the provinces of Battambang and Siem Reap. These territories had been reluctantly ceded to Cambodia earlier in the century. Although the Thai navy attempted these incursions, they were decisively defeated by the French, leading the Japanese to intervene and pressure the French into relinquishing the provinces for a nominal payment to save Thai face.

King Sisowath Monivong (r. 1927–41) held the French responsible for the territorial losses and refused to engage with them again, though his reign came to an end shortly thereafter. Following his death, the Japanese allowed the French to select a new king. In a bid for a more compliant ruler, they overlooked Monivong’s son and chose his inexperienced grandson, Norodom Sihanouk, who was crowned in September 1941.

Although the Japanese maintained a relatively hands-off approach in Indochina, they fostered anti-colonial sentiments to gain local support for their occupation. These nationalist feelings intensified after Japan’s surrender in August 1945, resulting in the dissolution of the French administration and setting the stage for significant changes in Cambodia’s political landscape. The period following the Japanese withdrawal marked a crucial turning point, as it led to a resurgence of national identity and the eventual push for independence from colonial rule.