Phu Quoc island

Phu Quoc, also known as Koh Tral in Cambodia, is the largest island in Vietnam. Phu Quoc, along with nearby islands and the remote Tho Chu Islands, is part of Kien Giang Province as Phu Quoc District, with a total area of 574 square kilometers and a permanent population of approximately 85,000 people. Phu Quoc District comprises the main island of Phu Quoc itself and 21 smaller islets. The district seat, Duong Dong, is located on the west coast and is the largest town on the island. The island's economy is centered around fishing, agriculture, and a rapidly growing tourism sector, with Phu Quoc being one of Vietnam's most famous tourist destinations.

An 1856 record mentions the island: "... King Ang Duong (of Cambodia) informed Mr. de Montigny, the French envoy visiting Bangkok, through the intermediary of Bishop Miche, of his intention to cede Phu Quoc to France. This proposal aimed to create a military alliance with France to counter the threat of Vietnam to Cambodia. However, this proposal did not receive a response from France.

As the war between Vietnam, France, and Spain was about to begin, Ang Duong sent another letter to Napoleon III to warn him about Cambodian claims on the lower Cochinchina region: the Cambodian king listed provinces and islands, including Phu Quoc, under Vietnamese occupation for several years or decades (in the case of Saigon, according to this letter, some 200 years). Ang Duong requested the French emperor not to annex any part of these territories because, as he wrote, despite the relatively long Vietnamese occupation, they remained Cambodian lands. In 1867, the Vietnamese authorities on Phu Quoc island pledged allegiance to the French troops who had just conquered Ha Tien.

After Cambodia gained independence from France, sovereignty disputes over the island arose due to the absence of a colonial decision on the island's fate. Dating back to 1939, the Governor-General of French Indochina, Jules Brévié, drew a line to delineate the administrative boundaries for islands in the Gulf of Thailand: those north of the line were placed under Cambodian protection; those south of the line were administered by Cochinchina. Brévié emphasized that this decision merely addressed police and administrative tasks, and no sovereignty decision had been made. Consequently, Phu Quoc remained under Cochinchina administration.

Phu Quoc mostly existed as a tranquil historical land. However, in the twentieth century, this island became involved in a series of attention-grabbing events.

After Mainland China fell into the hands of the Chinese Communist Party in 1949, General Huang Chieh moved over 33,000 soldiers of the Republic of China Army, mostly from Hunan Province, to Vietnam, where they were stationed on Phú Quốc. Later, in June 1953, the army moved to Taiwan. Currently, there is a small island in Chengcing Lake in Kaohsiung, Taiwan, which was constructed in November 1955 and named Phú Quốc Island to commemorate the loyal soldiers of the Chinese Nationalist Party who were detained from 1949-1953.

In 1967, during the period when Cambodia was under the rule of Sangkum Reastr Niyum (Sangkum Community), the country's ruler Norodom Sihanouk aimed to establish internationally recognized borders; specifically, in 1967, the government of North Vietnam recognized these borders. According to an article titled "Border Questions" published in the Kampuchea magazine in 1968 (and quoted on Sihanouk's website), this border definition acknowledged Phú Quốc Island as Vietnamese territory, even though Cambodia made sovereignty claims later.

On May 1, 1975, a Khmer Rouge squad raided and occupied Phú Quốc Island, but Vietnam quickly regained control of the island. This was the first event in a series of escalations leading to the Cambodian–Vietnamese War in 1979.