Chapter 74: The Nguyen-Trinh War and the Siamese Intervention
Since the late 16th century, the nominally united Dai Viet kingdom was divided between the Trinh and Nguyen families in the north and south respectively. Their role in Vietnamese politics began when Nguyen Kim and Trinh Kiem backed Le Trang Tong against the Mac dynasty that had recently usurped the throne, starting a struggle between the Later Le and Mac dynasties that lasted for decades until the latter was driven to Cao Da province in the far north in 1592. The two bloodlines developed a rivalry over the course of the century as they began to be established in their respective regions. During this time, the Trinh family established themselves as the puppet masters of the Le rulers. The near-complete defeat of the Mac dynasty ended any sense of unity as Trinh Tung tightened his grip on court affairs, leading to Nguyen Hoang adopting the princely title of Vuong and effectively declaring independence from Hanoi in 1600. The Nguyen lords in the south also began friendly relations with European merchants, particularly the Portuguese, and were producing their own bronze cannons from 1615 onwards. Finally, Nguyen Phuc Nguyen refused to pay taxes to Hanoi in 1620 and after a demand by Trinh Trang to submit fell on deaf ears, conflict broke out in 1627.
The first years of the war saw a continuous stalemate, with the Nguyen defenses and their bounty of advanced gunpowder weaponry and Portuguese advisors unable to be broken by the more numerous Trinh forces. However, an ever-changing web of alliances would alter the situation. Siam, an external foe of the Nguyen lords, began closer relations with the Spanish and Portuguese amidst rising Spanish-Japanese tensions, loosening Portuguese commitments to the Nguyen lords. The resulting Iberian-Japanese War would permanently weaken Portuguese presence in Southeast Asia, further weakening Portuguese ties with the family. Furthermore, the Trinh lords would take advantage of inter-European rivalries and turn to the ascendant Dutch for military aid. These changing circumstances would reflect upon the Battle of the Gianh River in 1643 when a Trinh army of 10,000, armed with the latest European cannons and arquebuses, broke through the Nguyen-constructed fortifications with the help of 5 VOC warships led by Pieter Baeck [1]. Although the land forces initially couldn’t break through the second and final wall, a successful Dutch victory at sea against a fleet of Nguyen junks enabled the 222-strong crew to make an amphibious assault from behind, forcing the encircled Nguyen army to retreat. This victory was followed by a successful siege of the Nguyen capital in 1646, forcing Nguyen Phuc Lan to flee further south with his supporters and relatives. The struggle between the two sides would continue but it was clear that the Trinh family had the momentum.
Gianh River in the modern day
It was at this low point when the Nguyen lords would swallow their pride and ask for assistance from a historical rival, Siam. By this time, Siam had taken advantage of the Viet infighting and once again made Cambodia its tributary while also defeating a Myanman attempt to wrest Lan Na from Siamese subjugation in 1637 [2]. Despite its success, however, the kingdom watched the Trinh momentum with alarm as a fully reunited Dai Viet under the rule of one family would no doubt pose a threat, particularly in retaining control over Cambodia and the Mekong Delta. Therefore, Prasat Thong was all too eager to intervene in the civil war and ensure the survival of a Nguyen-controlled south. At the capital of Ayutthaya, a large army was quickly gathered to be commanded in the field by the crown prince Chaofa Chai and his uncle Si Suthammaracha. They would be joined en route to southern Dai Viet by allied Cambodian troops. Combined, the Siamese intervention in the Trinh-Nguyen conflict involved 18,000 men.
With Siam jumping into the conflict, Trinh Trang knew he would have to muster a great army against the pro-Nguyen coalition. As the lord by now exceeded 70 years in age, he would have his son Trinh Tac lead any military campaign in the south. He himself would send his representatives into Cambodia and the lands of the Champa, hoping to trigger rebellion behind the backs of his enemy. The Trinh lord would also send an envoy to the VOC asking them for more assistance specifically against the Siamese. Before any of these other plans would come to fruition, however, the Trinh and Nguyen armies with their various allies would clash at Vijaya in 1649. The Nguyen-Siamese coalition army numbered 30,000 while the Trinh army numbered 25,000. Although the former held the numerical advantage, it was unbalanced in terms of skill. The Nguyen portion of the army, numbering around 12,000, had a disproportionate number of raw recruits due to heavy losses in the recent Trinh offensive while the Cambodians were the least well-equipped in terms of technological progress. By contrast, the Siamese had years of modernization and had many experienced men, most notably 2,000 samurai cavalry drawn from Kirishitan exiles and the retinue of the Honjo clan. The Nguyen forces formed the center while the Siamese composed the wings, the cavalry positioned on the right, and the Cambodian levies served as the reserves. Compared to their diverse foe, the Trinh army was relatively homogenous, equipped with many Dutch arquebuses and cannons with elephants in the middle of the army. Elephants were in the Trinh army as well, albeit more in the back.
Red=Cambodian, Salmon=Siamese, Blue=Nguyen, Brown=Trinh
Understanding that the soft spot of the coalition army was its center, Trinh Tac aimed his artillery inwards, disproportionately shelling the Nguyen center. This was followed by a charge from the center and almost immediately the Nguyen center began to be pushed back. The Siamese infantry on the left confronted the Trinh offensive only for the Trinh right to counter-charge, creating a stalemate. However, the cavalry-heavy left, fronted by the samurai cavalry contingent, was mopping up the Trinh left, only to be temporarily halted by the Trinh elephants. Nguyen artilleryfire, however, broke the elephants and they stampeded off the battlefield, throwing the Trinh ranks into disorder. Pressed on all sides, Trinh Tac ordered a retreat but not before suffering heavy losses. The battle ended in a clear Nguyen-Siamese victory with the Cambodian reserves not even having been deployed.
The victory at Vijaya completely changed the balance of power in Dai Viet, with the Nguyen lords backed by Siam beginning to recapture their lost lands. However, Trinh Trang’s machinations from afar began to kick in. 7 Dutch warships sailed near the bay of Ayutthaya and attempted a blockade, although the Siamese royal fleet were able to drive them out. Dutch ships would periodically harass the Siamese coastlines over the next few years without much material success while somewhat keeping the realm on their toes. The stirring within Cambodia aided by the activities of Trinh agents would prove to be a much more serious affair for the Siamese-Nguyen war effort. At the time, its ruler Ramathipadi I was controversially a Muslim in the Buddhist-majority kingdom, going by the name Ibrahim. This created much resentment among the populace and so were receptive to the Trinh-backed rebellion of Ang Non, a son of the late Outey and a Buddhist. The eruption of the rebellion and its initial success forced Siam to divert attention towards cracking down on Ang Non and his Trinh-backed supporters, halting the Nguyen reversal in southern Dai Viet. However, it wasn’t enough for Trinh forces to once again overwhelm enemy troops and Trinh Trang began to accept that a total victory was probably impossible. In 1652, after a quarter century of conflict, the Trinh and Nguyen lords finally agreed on peace, the latter recognizing the Le emperor in Hanoi once again while retaining autonomy through control of a reduced part of southern Dai Viet.
As for the Cambodian rebellion, Prasat Thong would resolve the situation by forcing Ibrahim off his throne, replacing him with Ang Non’s younger brother Ang So, crowned as Barom Reachea V of Cambodia in 1653. This reversed the momentum of Ang Non’s rebellion and it would conclude in 1655 with his death. Barom Reachea V’s new court in Oudong, unlike that of his predecessors, would see unprecedented levels of Siamese intrusion into Cambodian politics and encroachment upon the kingdom’s sovereignty. This fact, along with a weakened Nguyen realm, expanded Siamese political power in Indochina and increased the tripolarity of the region between them, the Myanma, and the Trinh lords.
[1]: The battle was a Nguyen victory IOTL.
[2]: Lan Na was never retaken by the Myanma in 1622.