Siamese-Vietnamese War

Siamese and Vietnamese leaders fought for control over Cambodia, with each seeking to install their own candidate as Cambodia’s new king. The two foreign powers clashed over the issue, until a rebellion in Vietnam forced the Vietnamese army home, leading to a brief peace favoring the Siamese.

Summary of Event

By the mid-eighteenth century, Siam and Vietnam were fiercely contesting their interests in Cambodia, the country lying between them. Siam had once been dominated by Cambodia, but it had since gained in power and now saw itself as the guardian of a dependent Cambodia. To lessen Siam’s influence over them in the early seventeenth century, Cambodian kings looked toward Vietnam, which was steadily expanding southward. In 1623, the Cambodian king Chey Chetta II married Ngoc Van, a famously beautiful Vietnamese princess, and invited Vietnamese settlers into southeast Cambodia. [kw]Siamese-Vietnamese War (Sept., 1769-1778)
[kw]War, Siamese-Vietnamese (Sept., 1769-1778)
[kw]Vietnamese War, Siamese- (Sept., 1769-1778)
Siamese-Vietnamese War (1769-1778)
[g]Southeast Asia;Sept., 1769-1778: Siamese-Vietnamese War[1950]
[g]Vietnam;Sept., 1769-1778: Siamese-Vietnamese War[1950]
[g]Thailand;Sept., 1769-1778: Siamese-Vietnamese War[1950]
[g]Cambodia;Sept., 1769-1778: Siamese-Vietnamese War[1950]
[c]Wars, uprisings, and civil unrest;Sept., 1769-1778: Siamese-Vietnamese War[1950]
[c]Diplomacy and international relations;Sept., 1769-1778: Siamese-Vietnamese War[1950]
[c]Expansion and land acquisition;Sept., 1769-1778: Siamese-Vietnamese War[1950]
Mac Thien Tu
Nguyen Phuc Anh
Ang Non
Rama I

Soon, internal dissent among Cambodia’s royal elite allowed Siam and Vietnam to deepen their influence within the country and to gain Cambodian territories in return for siding with rival Cambodian claimants to the throne. While Siam nibbled away at Cambodian lands in the west, the Vietnamese annexed much of the Mekong Delta. In 1679, the Vietnamese Nguyen lords who ruled the south welcomed an army of Chinese refugees who had opposed the new Manchu Qing Dynasty. These Chinese refugees were allowed to settle on the west coast of the new territories, facing the Gulf of Siam. Their northernmost outpost became the town of Ha Tien, right at the border to Cambodia, increasing Siamese-Vietnamese friction. A Cambodian war over royal succession led to the Siamese-Vietnamese clash of 1715, which ended with a Vietnamese victory.

In 1767, the Burmese captured and destroyed the Siamese capital of Ayutthaya, killing the king. Siam remained leaderless, until a military commander called Taksin defeated his enemies and crowned himself king in 1768. The son of a Chinese immigrant and a Siamese mother, Taksin had no noble blood, but his parents had given the boy to a Siamese aristocrat who had adopted him and raised him as a noble. Thus, when Taksin asked the new king of Cambodia, Ang Tong, for tribute, he refused, giving as his reason Taksin’s common origin. Taksin sent a punitive force to Cambodia in retribution, but the Cambodians defeated Taksin’s army by March of 1769.

The Cambodian king allied himself with Mac Thien Tu, the Vietnamese governor of Ha Tien and son of the late leader of the Chinese refugees who had settled there. In September, 1769, in an attempt to remove Taksin from power, Vietnamese troops led by Mac invaded southeast Siam. Mac attacked the Siamese towns of Trat and Chantaburi on the coast. He was victorious, until a plague broke out in his army, forcing the Vietnamese to retreat from Siam.

In 1771, Taksin launched his own invasion of Cambodia and the Vietnamese territory of Ha Tien. At the end of the autumn rainy season, Taksin sent about ten thousand Siamese soldiers to march overland into Cambodia from its western border with Siam. He embarked another force of ten thousand soldiers on warships sailing to Ha Tien. The Siamese army led by Taksin landed at Ha Tien and attacked the town. Since Vietnamese generals stationed in the Mekong Delta area refused to help Mac against the Siamese invaders, Taksin was able to conquer and destroy Ha Tien. He then moved up to meet his second army at the Cambodian capital of Phnom Penh.

At Phnom Penh, Taksin deposed Ang Tong and placed Ang Non on the Cambodian throne. A former Cambodian prince, Ang Non had escaped a plot to kill him by fleeing to Siam. He had then been caught in the burning of Ayutthaya but managed to escape, becoming Taksin’s friend in the process. Ang Tong, meanwhile, fled to the southern Vietnamese city of Gia Dinh (next to modern Saigon). He appealed for Vietnamese aid, and the Nguyen lords who ruled the south promised it to him.

In 1772, the Vietnamese counterattacked against the Siamese forces in Cambodia. Ten thousand Vietnamese troops supported by thirty galleys were sent against Taksin in Phnom Penh. Taksin burned the city and escaped with five hundred men to Ha Tien. His northern army, which had come by land, was also repulsed and forced to retreat. The Vietnamese reinstalled Ang Tong as king of Cambodia, but Ang Non fled with Taksin and refused to relinquish his claim to the throne.

In 1773, afraid for his life, Ang Tong tried to negotiate with Taksin to end Siamese support for his rival, but Taksin refused. Ang Tong retired to a small island in the middle of the Tonle Sap, Cambodia’s large inland lake. In southern Vietnam, the Tay Son rebels took the city of Qui Nhon, from which many of the Vietnamese soldiers fighting the Siamese had come. As the Vietnamese withdrew their army, Ang Tong abdicated in favor of Ang Non. To save face, Ang Tong insisted he acted out of pity for his Cambodian people, to save them from prolonged war, but historians insist it was the lack of Vietnamese troops protecting him that prompted him to step down.

As Ang Non was reinstalled as king of Cambodia, Mac Thien Tu negotiated a temporary end to hostilities with Taksin. In turn, Taksin withdrew his Siamese soldiers from Ha Tien. An uneasy armistice settled over the land. During the next few years, Tay Son Tay Son Rebellion (1771) revolts in southern Vietnam prevented the Vietnamese from engaging the Siamese, who controlled Cambodia through Ang Non. In early 1777, only Nguyen Phuc Anh survived and escaped when the Tay Son captured Gia Dinh and killed all other members of the Nguyen lords’ family. In the fall of 1777, however, Nguyen Anh recaptured Gia Dinh.

Nguyen Anh realized that internal Vietnamese stability was more important, for the moment, than control of Cambodia. Thus, to enable himself to focus his attention on the rebels threatening him, he sent a mission to Siam. In 1778, Nguyen Anh offered Siam a treaty of friendship that formally ended the war.


Because of the Tay Son Rebellion, the Vietnamese temporarily abandoned their anti-Siamese Cambodian policy. They agreed to a peace that left Siam in a dominant position in Southeast Asia. The conflict, however, would continue.

With a favorable peace in Cambodia, Taksin turned to Laos. He conquered Vientiane in a military campaign from November, 1778, to April, 1779. This campaign led the Vietnamese under Nguyen Anh to send soldiers into Cambodia to depose the hated “Siamese puppet” Ang Non. In 1779, Vietnamese and Cambodian troops captured Ang Non, drowned him in the Bassac River, and killed his sons. The Vietnamese installed the boy Ang Em, son of Ang Tong, as king. In 1780, the Vietnamese formally annexed the territory of Ha Tien when Mac Thien Tu died. With this addition to its territory, Vietnam reached its present shape and capped its southward extension.

Meanwhile, in response to quarrels over a Siamese vessel at Ha Tien in early 1780, Vietnamese living in the Siamese city of Thonburi were massacred in November, 1780. Taksin sent an army into Cambodia that captured Phnom Penh, shattering the Siamese-Vietnamese peace. Vietnamese interests were saved, however, when Taksin went mad and was forced to abdicate by popular revolt in March, 1782. Learning of these events at home, the leader of the Siamese army in Cambodia concluded a quick peace with Nguyen Anh and returned to Siam. There, he had Taksin beheaded on April 7, 1782, and crowned himself King Rama I. He founded the dynasty that still ruled Siam in the early twenty-first century. Siam once again controlled Cambodia.

In 1784, Rama I lent Nguyen Anh twenty thousand Siamese soldiers and two to three hundred warships to recapture Gia Dinh from the Vietnamese rebels. Many contemporary Vietnamese historians, who favor the Tay Son for their assumed revolutionary qualities, consider this to have represented a Siamese invasion of Vietnam. Indeed, the Siamese soldiers of Nguyen Anh behaved like conquerors, looting and plundering Vietnamese towns as they advanced.

Many Vietnamese historians see their ambush on the eve of the Tet festival on January 19, 1785, as an important national victory over Siam. Only two to three thousand Siamese soldiers survived to flee home. Never again did Nguyen Anh accept Siamese troops.

The friendship of Rama I and Nguyen Anh continued, however, and it kept Vietnamese-Siamese relations cordial for the remainder of the eighteenth century. Nguyen Anh even acknowledged Rama I as a vassal and sent him symbolic gifts from 1788 until 1801. He stopped this practice when he became the emperor Gia Long after his final victory in 1802.

Early in the nineteenth century, a unified Vietnam gradually wrested Cambodia from Siamese influence. After another Cambodian war of succession, Vietnam installed its choice of king and a military garrison at Phnom Penh in 1813. Until the French made Cambodia their protectorate in 1863, Vietnam rather than Siam dominated Cambodia.

Further Reading

  • Chandler, David. A History of Cambodia. 2d ed. Boulder, Colo.: Westview Press, 1992. Briefly discusses the detrimental impact of the war for Cambodia in the section “Vietnamese and Thai Interference in Cambodia.” Illustrated, maps, notes, bibliography, index.
  • Chapuis, Oscar. A History of Vietnam. Westport, Conn.: Greenwood Press, 1995. Briefly mentions the event in the context of Vietnamese land acquisition from Cambodia. Maps, bibliography, index.
  • Hall, Daniel George. A History of Southeast Asia. 4th ed. London: Macmillan Press, 1981. Still a standard work on the period. Chapters 24-25 and 27 cover events from Vietnamese, Cambodian, and Siamese points of view. Illustrations, maps, bibliography and index.
  • Terwiel, B.J. A History of Modern Thailand, 1767-1942. St. Lucia, N.Y.: University of Queensland Press, 1983. Strong focus on Taksin and Rama I; places the war in the context of Siamese history. Maps, notes.
  • Wyatt, David K., ed. Studies in Thai History. Reprint. Chiang Mai, Thailand: Silkworm Books, 1996. Collection of scholarly articles, some of which discuss leadership of Taksin and Rama I. Tables, footnotes.

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