Lao–Siamese War or the Siamese Invasion of Laos (1778–1779) was a military conflict between Thonburi Kingdom and the Lao kingdoms of Vientiane and Champasak. The war resulted in all three Lao kingdoms of Luang Phrabang, Vientiane and Champasak becoming Siamese tributary vassal kingdoms under Siamese suzerainty and domination in Thonburi and the subsequent Rattanakosin Period.
Background
Vientiane–Luang Phrabang Rivalry Succession disputes after the reign of King Sourigna Vongsa of Lanxang resulted in the fragmentation of the Lao kingdom of Lanxang into three distinct kingdoms of Luang Phrabang, Vientiane and Champasak in the early eighteenth century. In 1763, the Burmese armies under the new Konbaung dynasty invaded and captured Chiangmai and Lanna. The Burmese occupation of Lanna allowed the Burmese to expand its influences into Laos. In 1764, King Ong Boun of Vientiane sought alliance with the Burmese to invade his rival Luang Phrabang. The Burmese general Nemyo Thihapate led the Burmese army to attack the city of Luang Phrabang as a part of his campaign to conquer Ayutthaya. King Sotikakumman of Luang Phrabang defended his city but the Burmese shelled heavily. According to Burmese chronicles, the Burmese had the severed heads of Lao captives piled up into large collection of human heads to demoralize the Lao defenders. Luang Phrabang fell to the Burmese in March 1765. Both King Sotikakumman of Luang Phrabang and Ong Boun of Vientiane submitted themselves to become the vassals of Burma. The Lao kingdoms of Luang Phrabang and Vientiane then came under Burmese domination as vassal kingdoms. Sotikakumman also had to gave his daughter to become a consort of King Hsinbyushin and gave his younger brother Surinyavong to Burma as political captive. Nemyo Thihapate then proceeded to the south to attack Ayutthaya, leading to the Fall of Ayutthaya in 1767.
In 1767, two Lao brethren nobles by the name of Phra Ta and Phra Vo (Phra Vorarat), who had aided King Ong Boun on his ascension to the throne, rebelled against Ong Boun because they were refused the position of Upahad or heir as previously promised by Ong Boun. Phra Ta and Phra Vo established their new town called Nakhon Khueankhan (in modern Nong Bua Lamphu) and seceded from Vientiane. Ong Boun dispatched armies to deal with Phra Ta and Phra Vo but was unsuccessful. Ong Boun requested military aid from Phraya Nakhon Ratchasima (personal name Boonkhong) the Siamese governor of Nakhon Ratchasima and from the Burmese. After four years, Ong Boun managed to defeat the rebel brothers in 1771 with the aid of the Burmese and Siamese. Phra Ta was killed in battle, while his brother Phra Vo escaped to Don Motdaeng where he sought refuge under King Sayakumane of Champasak.
Also in 1771, Prince Surinyavong, who had been captured by the Burmese, took the throne of Luang Phrabang from his brother Sotikakumman and ascended as Surinyavong II. Surinyavong was vengeful of Ong Boun of Vientiane for his instigation of Burmese invasion of Luang Phrabang previously in 1765. As soon as he took the throne, Surinyavong marched his armies from Luang Phrabang to attack Vientiane. Ong Boun requested military support from the Burmese at Chiangmai against his rival. Ong Boun also informed King Hsinbyushin that, despite the Fall of Ayutthaya in 1767, Siam had recovered and regained momentum under the leadership of Phraya Tak or King Taksin. Hsinbyushin was then eager to initiate his new campaign against Siam and sent Nemyo Thihapate to attack Luang Phrabang first. Nemyo Thihapate, for the second time, led the assaults on Luang Phrabang. Surinyavong had to withdraw from Vientiane back to defend his own city. Nemyo Thihapate was able to take Luang Phrabang again and Surinyavong gave in. This time Ong Boun had to surrender his daughter to Hsinbyushin to be his consort in exchange for secured Burmese supports.
Relations between Siam and Vientiane King Taksin of Thonburi led the successful campaign to capture the Burmese-held Chiangmai in 1774–1775. After the Siamese capture of Chiangmai, the Burmese influences on Lao kingdoms waned. In his capture of Chiangmai in January 1775, Taksin found some Lao officials from Vientiane in Burmese armies, raising his suspicions about Vientiane being in cooperation with Burma. In 1775, King Taksin sent a diplomatic mission to King Surinyavong of Luang Phrabang to cement alliance. Surinyavong cordially accepted the friendly gesture from Thonburi. Taksin also sent a letter to Vientiane in 1775, rebuking Vientiane of its pro-Burmese stance. Taksin warned Vientiane to stop aiding the Burmese. Ong Boun replied in a letter to Thonburi that he had tried his best to live up to the alliance and was compelled to aid the Burmese because the Burmese had held his children in hostages. Ong Boun also offered to send his daughter Princess Nang Kaeo Nhotfa Kanlayani to be a consort of King Taksin. Taksin replied in a letter in February 1776 that he would send an entourage to escort the Lao princess to Thonburi next year but these marriage arrangements were not realized.
Invasion of Champasak (1777) In 1777, the governor of Nangrong had conflicts with Phraya Nakhon Ratchasima Boonkhong. Phraya Nangrong then decided to rebel against Thonburi with supports from Prince O and Prince In, who were nephews of King Sayakumane of Champasak. Nakhon Ratchasima sent reports to Thonburi about Nangrong. King Taksin then ordered Chaophraya Chakri to bring armies to Nakhon Ratchasima and captured Phraya Nangrong. Nangrong was tried and executed for his rebellion at Thonburi. Taksin also retaliated against Champasak for its support to Nangrong. He ordered Chaophraya Chakri and Chaophraya Surasi to march the Siamese armies from Nakhon Ratchasima to attack Champasak to the east in April 1777. The Siamese armies captured and sacked Champasak, Khong and Attapeu. However, the Siamese did not occupy nor vassalize Champasak on this occasion. This expedition served only to retaliate for Prince O and Prince In's support for Nangrong.
In May 1777, King Taksin raised Chaophraya Chakri to the rank of Somdet Chaophraya with the title of Somdet Chaophraya Maha Kasatsuk for his contributions to the successful campaigns. The rank of Somdet Chaophraya was the highest possible rank a Siamese noble could attain, with equal honor to a prince.
Phra Vo died in battle
For six years, Phra Vo enjoyed protection from Sayakumane of Champasak. In late 1777, Phra Vo came into conflicts with Sayakumane who had been his patron. Phra Vo decided to left Champasak and establish himself independent at Don Motdaeng. Phra Vo also sent his son Thau Kam to Nakhon Ratchasima to pledge alliance to Thonburi court and requested Siamese support. In the meantime, Ong Boun, informed about Phra Vo's separation from Sayakumane, sent Phaya Supho the supreme military commander of Vientiane to lead armies to attack Phra Vo at Don Motdaeng. Sayakumane refused to protect Phra Vo on this occasion. Phra Vo was overwhelmed and killed in battle in 1777. Phra Vo's son Thau Kam survived and informed Nakhon Ratchasima that his father had been killed by the Vientiane forces.
King Taksin, upon learning about the death of Phra Vo, was furious at Vientiane that Vientiane had unjustly killed Phra Vo, whom Taksin regarded as his subject. Taksin then initiate the punitive expedition against Vientiane. He ordered Chakri and Surasi to lead the Siamese armies of 20,000 men from Thonburi to Nakhon Ratchasima to invade Vientiane in December 1778. This Siamese Invasion of Vientiane, however, did not serve merely as to avenge for Phra Vo's death but as to strengthen Siam by moving against a Burmese ally and to acquire new vassal kingdoms. Taksin, on many previous occasions, had pretexts to invade Vientiane but he had been preoccupied with the Burmese to the west. At the end of Maha Thiha Thura's Invasion of Siam in 1776, Taksin was able to assign his forces to eastern frontiers. The death of Phra Vo became the casus belli for King Taksin to initiate his subjugation of Laos.
Siamese Invasion of Laos
Recruitment in Cambodia In Cambodia, the pro-Siamese king Ang Non was on the throne. From Nakhon Ratchasima, Chaophraya Chakri ordered his brother Chaophraya Surasi to go to Cambodia to raise an army composing of 10,000 Cambodian men to invade Vientiane from the south in another direction. Surasi reached Oudong in December 1778, where he informed King Ang Non about the Siamese plans. Ang Non then ordered Cambodian men to be gathered and levied from Kampong Svay, Srey Santhor, Preyveng and Tboung Khmum. Ang Non gave the 10,000 Cambodian men to Surasi for his campaign against Vientiane. The Cambodian king also promised to send further food supplies to support the Siamese. The Cambodians constructed boats and vessels for Surasi to proceed.
From Oudong, Chaophraya Surasi and his Cambodian army embarked on a riverine fleet and moved north upstream along the Mekong, passing the town of Sambour. The greatest obstacle was the Liphi waterfall (modern Somphamit waterfall), which used to mark the border between Lanxang and Cambodia. Surasi ordered Cambodian men to dig a new canal to circumvent the Liphi cascade. Chaophraya Surasi and his army finally were able to get through the obstacle and proceeded north towards Vientiane.
Lao–Siamese battles Phaya Supho, the Vientiane general who had earlier defeated Phra Vo, led the Lao defenses against the Siamese. Chaophraya Chakri and Phraya Nakhon Ratchasima Boonkhong marched from Nakhon Ratchasima to face the Laotians at Nong Bua Lamphu, leading to the Battle of Nong Bua Lamphu in December 1778. The Siamese prevailed, the Lao forces were defeated and Phaya Supho was compelled to retreat to Vientiane.
After passing through the Liphi waterfall, Chaophraya Surasi led his Cambodian fleet to attack Champasak. Champasak quickly fell. King Sayakumane fled the city but was captured by Siamese forces. Sayakumane was taken and brought to Thonburi.
Surasi then proceeded north along the Mekong to attack Nakhon Phanom (modern Thakhek, the town of Nakhon Phanom used to situate on the east bank of Mekong until it was later moved to the west bank to modern Nakhon Phanom in 1790 during the reign of King Rama I). Nakhon Phanom also fell to the Siamese in March 1779. Phra Borommaracha Kukeo the Lao governor of Nakhon Phanom fled the city and later died from illness.
Chaophraya Chakri from Nong Bua Lamphu and Chaophraya Surasi from Nakhon Phanom with the Siamese-Cambodian combined forces then converged on Vientiane. However, there were many surrounding vicinity towns of Vientiane that provided preliminary first-line defenses for Vientiane. Surasi took the Lao town of Nongkhai. Chakri and Surasi combined their forces to attack the Lao towns of Pakho and Viengkhuk (in modern Mueang Nong Khai district). Both Pakho and Viengkhuk resisted the Siamese considerably. Surasi then ordered many severed heads of Lao men from Nongkhai to be put in boat vessels and had Lao women to sail the boats to Pakho, announcing that they came there to sell the heads of Lao men. The Lao defenders of Pakho were then horrified by the cruelty of the Siamese and became demoralized. Pakho and Viengkhuk eventually fell to the Siamese in March 1779.
King Surinyavong of Luang Phrabang, upon learning about Siamese invasion of Vientiane, decided to pledge his alliance to Siam and contribute a force of 3,000 men to join the Siamese attacks on Vientiane. Chaophraya Chakri then ordered Phraya Phetchabun Pli the governor of Phetchabun to lead the Lao forces from Luang Phrabang to attack Vientiane from the north in the third direction.
Chakri pressed on to attack the town of Phanphrao (in modern Si Chiang Mai district), which situated on the Mekong just opposite of Vientiane. The Siamese were able to take Phanphrao and numerous Lao defenders died in battle.
Siege and Fall of Vientiane