Tây Thành () was formerly the 32nd province of Nguyễn Vietnam, encompassing what is now modern-day Cambodia. Its capital was the Cambodian capital of Phnom Penh (known to the Vietnamese as "Nam Vang"). It was a special province with a dual system, consisting of Cambodian monarchs who reigned as puppet rulers while a Vietnamese governor resided in Phnom Penh. The province was finally abolished in 1847 after peace talks between Siam and Vietnam concluded dual-suzerainty over Cambodia.
Context
In 1807, after Emperor Gia Long ascended to the throne, Emperor Chân Lạp Ang Chan II (Nak Ong Chan, Nặc Chăn) requested to submit to the court of Huế instead of the Siamese court as before.
Emperor Minh Mạng sent Trương Minh Giảng, Phan Văn Thúy with troops to quell the rebellion of Lê Văn Khôi. Taking advantage of the high walls and deep moats, Lê Văn Khôi's forces effectively held out. The imperial army besieged the fortress for two years before finally breaking through in September 1835. Lê Văn Khôi had died from illness before that, and his son and remaining followers were captured and executed.
Meanwhile, the Siamese forces attacked An Giang province (in December 1833), then advanced to engage in battle at Củ Hủ.Củ Hủ, also known as Cù Hu or Cổ Hổ, is a canal flowing through Tứ Điền village in the Chợ Thủ area, now located in two communes, Long Điền A and Long Điền B, Chợ Mới district, An Giang province. In this battle, the Nguyễn court's army won and launched a counterattack to reclaim the Châu Đốc post in An Giang province, then the Hà Tiên fortress, and together with the forces of pro-Vietnamese Cambodian, they moved upstream on the Mekong River to retake the Nam Vang citadel. The Siamese army was defeated and forced to withdraw from Cambodia; the imperial court in Huế then restored Ang Chan II to the throne.
After driving out the Siamese forces, Trương Minh Giảng and Lê Đại Cương established a post at Đại Nam near Nam Vang to protect Chân Lạp. The governance within Chân Lạp was entirely arranged by Vietnamese officials, while the Chân Lạp court's ministers only took on minor tasks.
At the end of 1834, the king of Chenla, Ang Chan II, died without a son, and the governance within the country fell to several local officials, including Trà Long (Chakrey Long) and La Kiên,Đại Nam thực lục records them as Chưởng cơ Trà Long and Vệ uý La Kiên who were originally from Chân Lạp but had been granted official titles by the imperial court in Huế.
In 1835, Trương Minh Giảng petitioned the emperor to appoint the daughter of Nặc Ông Chân, Ang Mey (Ngọc Vân), as a princess, called Chân Lạp Princess. In reality, Ngọc Vân had no real power.
In 1836, Emperor Minh Mạng changed the name of Chân Lạp to Trấn Tây and officially annexed it into Đại Nam. The northwestern border of Trấn Tây extended to the Tonlé Sap lake.
The Nguyễn Dynasty's Direct Rule Administrative Management Trấn Tây Thành was divided into 33 provinces and 2 districts: "The Relationship between Vietnam - Cambodia - Siam from 1834 to 1848" Đại Nam thực lục, Volume 4, Official History, Second Period (1834-36)
The Huế court abolished the native official titles of Chân Lạp and applied the official system of the Nguyễn Dynasty. Lê Đại Cương (later replaced by Dương Văn Phong) was appointed as the Chief Counselor, and a military commander, four main and deputy military officers were appointed. Various other positions were established, including hiệp tán, đề đốc, lang trung, viên ngoại lang, giáo thụ, and huấn đạo. In strategic areas, the positions of tuyên phủ and an phủ were also created for defense.
In 1840, the emperor appointed Lê Văn Đức as the imperial envoy, with Doãn Uẩn as his deputy, and together with Trương Minh Giảng, they were tasked with overseeing all matters in Trấn Tây Thành, inspecting trade activities, measuring land, reassessing the poll tax, and taxes on river-based trading boats.
Emperor Minh Mạng ordered a census of the population in Chân Lạp, which had just been annexed into the territory of Đại Nam. The population was recorded at 970,516 people, while the land area amounted to 4,036,892 acres.Minh Mạng chính yếu. Chuyện đường rừng, p. 21-22
Map of Vietnamize Names in Cambodia
Relations with the Natives
When the Nguyễn Dynasty conquered Nam Vang and appointed Ang Chan II as the king of Chenla, his siblings Ang Snguon, Ang Em, and Ang Duong fled the city and sought refuge with the Siamese forces at Vọng Các. The Siamese court took advantage of this situation and attempted to bring them back to Chenla to contest the throne with Ang Chan, aiming to restore Siam's influence over the region.
Meanwhile, in Trấn Tây, the Nguyễn Dynasty conferred titles on the three daughters of Ang Chan II: Ang Pen (Ngọc Biện 玉卞, Brhat Anak Angga Ang Baen) (1809-1840) was made the military commander of Lư An;(a district in Trấn Tây) Ang Mey (Ngọc Vân 玉雲, Samdach Brhat Anak Angga Mei Khieu) (1815-1874?) was appointed Chân Lạp Princess, succeeding her father's throne; Ang Snguon (Ngọc Nguyên 玉源) (1829-1875) was made the military commander of Tạp Ninh;(a district in Hải Đông) Ang Pou (Ngọc Thu 玉秋, Samdach Brhat Maha Uparajini Puyani) (1822-1878) was made the military commander of Thâu Trung.(a district in Hải Tây)
In 1839, Ang Em and Ang Duong brought 9,000 Khmer people along with 70 boats from Battambang (Siamese-occupied territory) to Trấn Tây (the region governed by Đại Nam), intending to ask the Nguyễn Dynasty court to allow them to succeed Ang Chan as king. However, they were captured by Trương Minh Giảng. The court ordered that Ang Em be brought to Gia Định for interrogation, then sent to Huế for imprisonment.
In 1840, Trà Long (Chakrey Long),Minister of War Nhân Vu (Yumreach Hu),or Nhâm Vu. Yomreach (ឧកញ៉ាយោមរាជ - Nhum Rạch) - Minister of Justice and La Kiên came to Huế to celebrate the emperor's birthday. However, they were charged by the emperor, imprisoned, and exiled to Northern Vietnam. Meanwhile, in Trấn Tây, the Chief Counselor Dương Văn Phong charged Ngọc Biện (Ang Baen), the sister of Princess Ngọc Vân, with treason for allegedly attempting to escape to Siam, and she was sentenced to death. Later, Trương Minh Giảng arrested Ngọc Vân and her two sisters, Ngọc Thu and Ngọc Nguyên, and placed them under house arrest in Gia Định. Many Vietnamese officials who came to Trấn Tây engaged in illegal activities, abusing their power and exploiting the local population. Đại Nam thực lục (Second Period - Volume CCXIX - 219): The administrative official Trần Văn Triện submitted a petition stating that the local bandits in Trấn Tây had caused disturbances, but after thorough investigation, it was found that the real cause was the misconduct of various Vietnamese officials who improperly governed the people, such as Vũ Hành, the governor of Hải Tây, who extorted bribes from local leaders, forced the daughters of citizens into servitude, and Lê Bá Hùng, the district chief of Trung Hà, who seized irrigation resources for personal gain and set up unauthorized military posts, demanding that merchants pay tribute. Additionally, Vietnamese soldiers oppressed the indigenous people, leading to numerous abuses and grievances.
The king said: “Currently, we are in the midst of military campaigns, so it is not appropriate to summon for investigations. However, I have already given instructions for each person and each matter. If we leave these unresolved, those who have committed offenses will not be deterred. Therefore, Vũ Hành and Lê Bá Hùng are to be immediately relieved of their positions, detained, and handed over to Doãn Uẩn and Cao Hữu Dực for thorough and strict investigation.” These two officials were later sent to Trấn Tây to serve as soldiers.Quốc sử quán triều Nguyễn, Đại Nam thực lục (tập 05). Bản dịch của Trung tâm khoa học xã hội và nhân văn quốc gia, Viện sử học Quốc sử quán triều Nguyễn, Tổ Phiên dịch Viện Sử học phiên dịch. Nhà xuất bản Giáo Dục xuất bản năm 2007.
With an arrogant attitude and disdain for the officials of Chân Lạp, this caused widespread discontent among the people, making the administration of Trấn Tây increasingly difficult. The people of Chân Lạp found a reason to rebel, attacking and causing turmoil everywhere, opposing the Việtization policies of the Huế court. Ang Chan’s younger brother, Ang Duong, took advantage of this situation to rise in rebellion, and with support from Siam, intervened in the internal affairs of Chân Lạp. Consequently, the imperial forces in Trấn Tây had to constantly fight to suppress the uprisings, which drained their military resources.
In 1840, several thousand Siamese troops marched into U Đông (Oudong). King Minh Mạng sent generals Phạm Văn Điển and Nguyễn Tiến Lâm with forces to confront them, but they were unable to break the siege.
It was not until the reign of Emperor Thiệu Trị that it was discovered that Ngọc Biện had been wrongfully convicted.Quốc sử quán triều Nguyễn, Đại Nam thực lục, Chính biên, Đệ tam kỷ, quyển 06: "Xưởng lại tâu : “án của Ngọc Biện khi trước, do Dương Quan Thảo thêu dệt ra, Dương Văn Phong khép buộc vào, Trương Minh Giảng không chịu xét đến căn nguyên, nhất vị y theo, để cho được Ngọc Biện phải chịu oan, bọn thổ dân tức giận, việc biến loạn ở Trấn Tây ngày nay chính là do án ấy khêu gợi ra vậy”. Vua đem việc ấy hỏi Doãn Uẩn, Uẩn thưa rằng : “Thần không dự biết án ấy, chỉ nghe thấy Lê Văn Đức có nói : Ngọc Biện chịu ơn triều đình rất hậu, có gì lại mưu trốn đi, tình cũng đáng ngờ. Vua phán : “Trong việc ấy tất có duyên cớ, nếu không thì Phan Văn Xưởng đâu dám khiếu oan cho con ma người Man, hãy tạm để việc ấy đấy”.Quốc sử quán triều Nguyễn, Đại Nam thực lục (tập 06). Bản dịch của Trung tâm khoa học xã hội và nhân văn quốc gia, Viện sử học Quốc sử quán triều Nguyễn, Tổ Phiên dịch Viện Sử học phiên dịch. Nhà xuất bản Giáo Dục xuất bản năm 2007. In addition, at the end of Minh Mạng's reign (1840), Lê Quang Huyên, the governor of Hà Tiên, intercepted a letter from the people of Chân Lạp complaining about the oppression they suffered under Trấn Tây General Trương Minh Giảng. The letter also mentioned the harassment by tax collectors and the unjust demands, including Trương Minh Giảng's attempt to marry Princess Ngọc Vân (Ang Mey). These grievances added to the unrest in the region.Quốc sử quán triều Nguyễn, Đại Nam thực lục (tập 05). Bản dịch của Trung tâm khoa học xã hội và nhân văn quốc gia, Viện sử học Quốc sử quán triều Nguyễn, Tổ Phiên dịch Viện Sử học phiên dịch. Nhà xuất bản Giáo Dục xuất bản năm 2007.Đệ nhị kỷ - quyển CCXX - 220, Thực lục về Thánh tổ nhân hoàng đế, Canh Tý, Minh Mệnh năm thứ 21 , mùa đông tháng 12:
Quyền lĩnh Tuần phủ Hà Tiên Lê Quang Huyên reported that the spies had found a letter from the Chân Lạp people, which accused Trấn Tây Tướng quân Trương Minh Giảng and the tax collectors of exploiting the locals by demanding gold. The letter, which was written in inappropriate language, was translated into Chinese and submitted to the court.
The Quảng Biên administration reported that the rice fields were ripening, and that the bandits were still spreading trouble. However, in the Khai Biên region, no bandits had gathered. Additional troops had been sent to work with Lê Quang Huyên, the Defense Supervisor Phạm Văn Sỹ, and other forces to track down and eliminate the remaining rebels, setting up posts in vulnerable areas to prevent foreign threats.