[7][8][9] King Rama also carved Northwestern Cambodia, including Battambang and Siemreap, for Chaophraya Aphaiphubet, a pro-Siamese Cambodian minister, to govern under direct Siamese control.

Ang Chan refused to attend the funeral of the Siamese King Phuttha Yotfa in 1809, executing his pro-Siamese ministers and taking anti-Siamese stance.

[7] The Vietnamese Emperor Gia Long assigned Lê Văn Duyệt to restore Ang Chan to the Cambodian throne in 1813.

[7] In 1819, Gia Long ordered the construction of Vĩnh Tế canal that connected Châu Đốc and Hà Tiên on the Cambodian–Vietnamese border,[5] putting Cambodian people into the labor works.

The Siamese quickly took Hà Tiên, Châu Đốc (An Giang province) and proceeded along the Bassac river invading Southern Vietnam, crossing the Vàm Nao canal into the Mekong heading towards Saigon.

Unable to break through Vietnamese blockade, Chaophraya Bodindecha decided to retreat along with his Siamese forces to Châu Đốc and Phnom Penh.

Minh Mạng ordered his minister Lê Đại Cương to bring the Cambodian king Ang Chan to return to Phnom Penh to resume the rule.

Vietnamese bureaucracy was introduced into Cambodia, superseding indigenous Cambodian noble-aristocracy, which still existed but was deprived of actual administrative roles.

[16] Trương Minh Giảng ordered Chauvea Tolaha Long the pro-Vietnamese Cambodian Prime Minister to march against Snang Ey at Kampong Svay.

Phrakhlang moved the city of Chanthaburi five kilometers to the upland position for better defensive site and constructed the Noenwong Fort (Thai: ป้อมเนินวง).

In December 1838, Ang Em defected from Siamese tutelage to Vietnam and arrived in Phnom Penh in the hope that Trương Minh Giảng would make him king.

[20][21][5] In November 1840, the Siamese warlord Chaophraya Bodindecha sent troops led by his son Phra Phromborrirak and his brother-in-law Chao Phraya Nakhon Ratchasima Thongin from Sisophon to lay siege on Pursat, which was held by Vietnamese forces.

Bodindecha then negotiated a peaceful surrender with Võ Đức Trung[10] the military commander of Pursat on December 31, 1840, before Trương Minh Giảng could reach him.

However, Bodindecha was now unopposed and sent his son Phra Phromborrirak to help Prince Ang Duong to the throne in Oudong and to massacre all remaining Vietnamese people still dispersed in Cambodia.

[1] After Siamese dominance was established in Cambodia, King Rama III ordered the Vĩnh Tế Canal at the Cambodian-Vietnamese border, which enabled Vietnamese naval forces to access the Gulf of Thailand quickly.

The king thus sent his half-brother Prince Isaret (later Viceroy Pinklao), accompanied by Chuang Bunnag (son of Phraklang, later Somdet Chao Phraya Sri Suriyawongse) and five brigantines to attack Hà Tiên (Banteay Meas) and a land force, led by Chao Phraya Yommaraj Bunnak and Prince Ang Duong, to attack An Giang Province.

Chuang Bunnag led the Siamese brigantines to attack Hà Tiên and sent a Cambodian force to take Cô Tô Mountain on March 10, 1842.

Chuang then visited Prince Isaret at Phú Quốc, who decided to retreat on March 26 because of the overwhelming Vietnamese numbers and the unfavorable winds.

Nguyễn Công Nhân was unable to repel the Siamese attacks, and Thiệu Trị sent Tôn Thất Nghị with reinforcements.

Chao Phraya Yommaraj Bunnak and the Siamese were defeated at Châu Đốc on April 8, 1842, suffering heavy losses, and retreated to Phnom Penh.

[10] The Siamese campaigns of 1841 had failed to bring about lasting peace but greatly devastated and depopulated large areas of central, south, and southeastern Cambodia, which antagonized many Cambodians.

Upon learning of the abortive plot, Emperor Thiệu Trị launched an offensive into Cambodia in three groups[citation needed] with Võ Văn Giải, the governor of Gia Định Province and Biên Hòa Province as supreme commander;[5] After Prince Ang Duong had the outspoken Vietnamese sympathizers at his court executed in May 1845, the armies began to advance in July 1845.

Nguyễn Văn Hoàng marched along the Bassac River and, after he had defeated a Cambodian contingent at Preak Sambour, proceeded to Ba Phnum.

Chaophraya Bodindecha left Bangkok on July 25, 1845, with his forces and hurriedly marched via Battambang to Oudong to defend the Cambodian royal capital.

[10] Nguyễn Văn Chương led about 20,000 Vietnamese troops and 1,000 warships, divided into many smaller forces, expecting to attack and besiege Oudong from all directions, which was defended by Bodindecha and Duong.

[1] In December, after some further minor clashes between Siamese-Cambodian forces with the Vietnamese command post in Kampong Luong, both sides agreed to negotiate.

[27] Doãn Uẩn requested for Prince Ang Duong to send a mission to Huế, to apologize, and to submit to Vietnamese rule.

King Rama III granted Chaophraya Bodindecha permission to negotiate for peace terms by himself on behalf of Siamese royal court.

Nguyễn Tri Phương, who was then the superintendent of six provinces in Cochinchina, sent a formal letter to Chao Phraya Sri Suriyawongse asking for the return of Vietnamese captives from the war ten years earlier.

Sri Suriyawongse replied that those Vietnamese were already settled down in Siam and he instead returned the seized muskets and ammunition[28] to Nguyễn Tri Phương.