Early interactions

Japan's relationship with Cambodia began in 1603.^[1] Cambodian ships would trade at the port of Nagasaki. In one of Cambodia's earliest mission, military aid was requested. Tokugawa Ieyasu sent swords and other weapons. However, Ieyasu did not want to be involved in Southeast Asian military actions.

In 1742, official contact with Japan and Cambodia ended. Cambodian officials stopped going to Nagasaki for trade.

Throughout 18th and 19th century, constant wars in Cambodia (from civil wars and rebellions to wars between Vietnam and Siam Empire) further prevented Cambodia and Japan from resuming relations.

World War II

During World War II, the Franco-Thai War in 1940 weakened the colonial regime in French Indochina. The Hitlerian puppet regime Vichy France signed an agreement with Imperial Japan to allow military transit through French Indochina.

Taking advantage of Thailand's friendship with Japan and the weakened situation in France, Thai government under pro-Japanese leadership of Plaek Phibunsongkhram invaded Cambodia's western provinces.

In March 1941, Tokyo hosted the signature of a treaty that formally compelled the French to relinquish the provinces of Battambang, Siem Reap, Koh Kong as well as a narrow extension of land between the 15th parallel and the Dangrek Mountains in Stung Treng Province. As a result, Cambodia had lost almost half a million citizens and one-third of its former surface area to Thailand.

In August 1941, Imperial Japanese Army entered the French protectorate of Cambodia and established a garrison that numbered 8,000 troops. Despite their military presence, the Japanese authorities allowed the cooperating Vichy French colonial officials to remain at their administrative posts.

Kingdom of Kampuchea

On 9 March 1945, during the closing stages of the war, Japan overthrew the French rule in Indochina.

On 13 March 1945, Norodom Sihanouk The King of Cambodia proclaimed an independent Kingdom of Kampuchea following Japan formal request. Shortly thereafter, Japan nominally ratified the independence of Cambodia and established embassy.

On 18 March 1945, Sihanouk himself also served as Prime Minister. However, Son Ngoc Thanh, who previously fled to Japan following the 1942 anti-French demonstrations, had returned in April 1945 to serve as foreign minister. Son Ngoc Thanh became prime minister following the surrender of Japan, serving until French colonialism returned in October 1945.

With the surrender of Japan in August 1945, the Allies disarmed and repatriated soldiers of Imperial Japan. The French were able to reimpose the colonial administration in Phnom Penh in October the same year.

On 12 October, French colonial authorities exiled Son Ngoc Thanh to France and put him under house arrest due to his collaboration with Japan in World War II. However, his supporters went underground and joined forces with Khmer Issarak, where both they and Japanese holdout got involved in First Indochina War.

Cold War Era

In January 1953, Japan and Cambodia again established formal diplomatic relations, with Norodom Sihanouk The King of Cambodia being awarded Order of the Chrysanthemum in 1955 by Hirohito The Emperor of Japan.

Relations continued even after Lon Nol and his faction launched a coup in 1970 that overthrown the kingdom and created US puppet regime Khmer Republic, although technically Japan still recognized the exiled Sihanouk as the king of Cambodia.

In 1975, embassies of both sides were closed due to the rise of communist regime Khmer Rouge. As Pol Pot regime collapsed in the wake of Third Indochina War, the FUNSK established People's Republic of Kampuchea, however they and Japan did not contact each other.

After Cold War era, the Embassy of Japan in Cambodia resumed operations in 1992, and the Embassy of the Kingdom of Cambodia in Japan resumed operations in December 1994.