Cambodia continued as a protectorate of France from 1863 to 1953, administered as part of the colony of French Indochina, though occupied by the Japanese empire from 1941 to 1945. After King Norodom's death in 1904, France manipulated the choice of king and Sisowath, Norodom's brother, was placed on the throne. The throne became vacant in 1941 with the death of Monivong, Sisowath's son, and France passed over Monivong's son, Monireth, feeling he was too independently minded. Instead, Norodom Sihanouk, who was eighteen years old at the time, was enthroned. The French thought young Sihanouk would be easy to control. They were wrong, however, and under the reign of King Norodom Sihanouk, Cambodia gained independence from France on November 9, 1953.

Cambodia became a constitutional monarchy under King Norodom Sihanouk. When French Indochina was given independence, Cambodia lost official control over the Mekong Delta as it was awarded to Vietnam. The area had been controlled by the Vietnamese since 1698 with King Chey Chettha II granting Vietnamese permission to settle in the area decades before.