Cambodia was once a much larger kingdom called Angkor, and was strongly influenced by Buddhism and Indian civilization. The Khmer people are a major ethnic group in Cambodia and speak a language also known as Khmer. Their history of being victimized by aggressive neighbors engendered a persistent suspicion among the elites and commoners of Cambodia that there existed Thai and Vietnamese designs to conquer/colonize Cambodia. Such worries surfaced again during the 1970s, and would be taken advantage of by the Khmer Rouge.
France made Cambodia into a French protectorate in 1863 and amalgamated parts of Vietnam and Laos into an entity called “French Indochina”. In 1940, the French put a 19-year-old prince named Norodom Siihanouk on the throne because they thought he could be more easily manipulated.
Japan gained control over Cambodia during WWII but did not have to use military force to gain control over French Indochina, and thus Japan is not considered to have formally colonized this region. Instead of using military force, they signed an agreement with the French government to let Japan station and move troops through its colonies in Indochina in exchange for allowing French colonial administrators to remain in their posts. In March of 1945, the Japanese encouraged the local elite in the “French Indochina” region to declare their independence; King Sihanouk did so, but the French soon returned to successfully re-colonize Indochina.
The First Indochina War lasted from 1946 to 1954, and was an anticolonial conflict that the Vietnamese fought against the French. During this time, starting in 1953, Sihanouk embarked on a world tour to promote independence for Cambodia. Bogged down by the war in Vietnam, the French granted independence to both Cambodia and Laos as they were considered less important than Vietnam. However, this independence was incomplete – France retained the right to control the economies and foreign relations of the two countries. Eventually, the 1954 Geneva Agreements that settled the First Indochina War did affirm Cambodian full independence and territorial integrity.
King Sihanouk abdicated the throne in 1955 to participate in politics, and in the process, installed his father as the ceremonial head of state. Sihanouk’s politics kept Cambodia neutral during the Cold War, broke off diplomatic relations with the U.S. in 1967, maintained peaceful relationships with China as he thought it would become the dominant power in Asia, and dealt harshly with the communists in Cambodia.