In 1281, after conquering much of Central Asia, Eastern Europe, and Dila (in China), the Mongols sought to pass through Đại Việt (the former name of Vietnam) to attack the Song dynasty from the south. They repeatedly sent envoys, demanding that Đại Việt improve its roads and allow their armies to pass through. Suspecting this was a pretext for invasion, the Trần emperor refused and imprisoned the envoys. Angered, the Mongol dynasty decided to invade Đại Việt. Confident in their superiority, they sent 50,000 troops, believing this was more than enough for such a small nation. Among the Mongol forces were some of their best military leaders, including Uriyangqatai, Quaidu, and Abiska, along with royal family members.
Meanwhile, Đại Việt had been preparing for war. Observing the Mongols’ growing threat, they gathered intelligence through their ambassadors in Song China. After the Song lost control of the southern regions near the Đại Việt border, bandits created instability, even attacking Đại Việt civilians. In 1241, Đại Việt’s king led an army into Song territory, gaining land and placing General Trần Khuê Bình in charge. This move likely aimed to gather intelligence on the Mongol forces. With a strong military tradition, especially in naval power and war elephants, Đại Việt was ready for battle. The Vietnamese spirit to resist Mongol invasion was strong, backed by both preparation and experience.
Major battles
The battle of Bình Lệ Nguyên
War elephants were a key military strength of Đại Việt, renowned for their use in battle throughout its history. Since horses were generally terrified of elephants, Đại Việt leaders strategically chose to deploy their troops at Bình Lệ Nguyên, a flat terrain ideal for elephant warfare, despite knowing the Mongolian cavalry’s formidable reputation.
Mongol Strategy:
The Mongols planned a multi-pronged attack. The vanguard, led by Cacakdu, aimed to cross the Phan River, seize Đại Việt’s ships, and block their retreat. Uriyangqatai advised caution, instructing Cacakdu not to engage immediately, but to focus on capturing the ships. Meanwhile, the main Mongol force of 30,000 soldiers, commanded by Uriyangqatai, would directly engage Đại Việt’s army. To minimize Mongol casualties, surrendered Dali soldiers were placed at the front to absorb Đại Việt’s initial counterattacks. Finally, Quaidu, leading 5,000 elite cavalry, would attack Đại Việt’s flanks and cut off their retreat by separating the vanguard from the rear guard.
The goal was to prevent Đại Việt reinforcements and ensure a quick victory by capturing the Đại Việt King in one decisive battle.
The Battle:
However, the battle did not unfold as Uriyangqatai planned. After crossing the river, Cacakdu’s forces were spotted and engaged by Đại Việt’s rear guard before they could capture the ships. Reinforcements continually arrived to support Đại Việt, and Cacakdu’s mission failed. Seeing the dust from the battle, Uriyangqatai sent reinforcements. As the Mongols crossed the river, the Đại Việt King unleashed a charge with war elephants, supported by infantry and cavalry.
The surrendered Dali soldiers bore the brunt of the elephant attack, while the Mongol cavalry struggled against the mighty beasts. Đại Việt troops rained arrows from atop the elephants and used long-handled weapons to engage the Mongols. The Mongol formation fell into chaos, with horses panicking and disorder spreading. Initially, the Vietnamese forces gained the upper hand due to their knowledge of the terrain and the elephants’ impact on the battlefield.
However, the Mongols adapted quickly. Aju, a Mongol commander, split his cavalry into two groups and ordered them to target the elephants’ eyes and trunks, as well as their riders. Expert Mongol archers neutralized the elephants, turning them from an asset into a liability for Đại Việt. Some elephants panicked and trampled Vietnamese soldiers, giving the Mongols the opportunity to showcase their superior archery and regain control of the battlefield.
Đại Việt King’s Role:
The Đại Việt King, a brave and hands-on leader, participated in the battle alongside his generals, putting himself at great risk. As the Mongols closed in, Lê Tần, a loyal general, advised the King to retreat, warning that fighting to the end would be disastrous. This decision proved wise; although the King ordered a withdrawal, the Mongols pursued him relentlessly. Near Cụ Bản, General Phạm Cự Chích and his local troops provided crucial support, slowing the Mongol advance but suffering heavy casualties, including the general himself.
Despite setbacks in the initial battle, Đại Việt’s withdrawal strategy laid the groundwork for a successful counterattack, leading to the eventual expulsion of the Mongols from the capital after only 19 days.
The battle of Phù Lỗ
During the withdrawal, the Đại Việt forces collapsed the Phù Lỗ Bridge to delay the Mongol pursuit. Phú Lương Hầu was tasked with leading a small unit to hold off the advancing Mongols. The Mongols used a clever technique to assess the river’s depth: they shot arrows high into the air, allowing them to fall into the water. If the arrows sank and then floated, the water was too deep for their cavalry to cross; if the arrows did not float, the water was shallow enough for them to pass. This method surprised the Vietnamese troops.
After discovering a shallow crossing, the Mongols quickly moved their cavalry across the river. Phú Lương Hầu’s small force fought valiantly but could not hold off the Mongols for long. The Mongols eventually caught up with the main Đại Việt forces at another river, sinking a few of their vessels, but they failed to capture the Đại Việt King. In frustration, the Mongol general ultimately committed suicide.
Despite their losses, the Trần leadership recognized that they had underestimated the Mongols. While Đại Việt troops were well-trained, the Mongols had years of experience and highly skilled cavalry. The use of war elephants proved disadvantageous against Mongol archery. However, the battle also showcased the discipline and resilience of the Vietnamese army. Even in the face of adversity, they withdrew in an orderly fashion, not in panic, maintaining control amidst their enemy.
Uriyangqatai was enraged by their failure to capture the King and the successful retreat of many Vietnamese troops. He blamed Cacakdu for the outcome, leading to Cacakdu’s suicide. What the Mongols did not realize was that Đại Việt’s swift retreat was due to well-prepared ships. The Mongols’ moment of satisfaction would soon fade, as more surprises awaited them.
The surprise for the Mongols at Thăng Long capital
Initially, the Mongols found their advance easy, but upon reaching the capital, they were met with an empty city, except for their imprisoned envoys. There were no people, no food—nothing. This was a premeditated strategy by Đại Việt, not a reaction to losing the battle. Moving such a large population, including elderly, women, and children, faster than the Mongols could advance would have been impossible without planning.
While the King led the army in battle, Lady Linh Từ had already evacuated the royal family, officials’ families, and civilians to safety. The evacuation was remarkable, moving thousands of people, soldiers, and valuable resources using Vietnam’s strong aquatic capabilities. When the Mongols arrived at the deserted capital, they planned to stay and subjugate the Vietnamese but were met with disappointment.
The Mongols typically carried limited provisions, expecting to seize food from the regions they conquered. In Đại Việt, however, they found nothing. The people had taken or hidden all the food, leaving the Mongols in a dire situation. Frustrated, they resorted to killing the few remaining inhabitants and destroying the city, igniting Vietnamese resolve.
Desperate for supplies, the Mongols raided nearby villages, but the locals, following Trần Thủ Độ’s orders, had prepared defenses, buried their food, and set traps. In places like Cổ Sở, villagers used spikes, trenches, and arrows to repel Mongol attacks, preventing them from looting effectively. With food running low and faced with fierce resistance, Uriyangqatai feared a counterattack and withdrew to Đông Bộ Đầu.
Meanwhile, the Vietnamese troops, well-supplied thanks to Đại Việt’s strong agricultural foundation, remained unshaken. However, the Mongols’ brief occupation of the royal capital caused anxiety. After the withdrawal, the King sought counsel from his brother, Trần Nhật Hiệu, who, paralyzed by fear, advised fleeing to the Song Dynasty in China. Disappointed, the King turned to his uncle, Trần Thủ Độ, who reassured him with unwavering confidence, saying, “As long as my head remains, Your Majesty, there is no need to worry!”
The decisive battle of Đông Bộ Đầu
The Vietnamese possessed a wide variety of vessels, each designed for different combat purposes. In certain situations, the sailors themselves could take up arms and join the fight. Ten days after the battle of Bình Lệ Nguyên, the Vietnamese launched a counterattack against the Mongols. The 18-year-old Crown Prince Trần Hoảng was appointed to lead the vanguard on a warship, while the King commanded the rest of the forces.
After nearly a week of suffering in Thăng Long, enduring a battle unlike any before, the Mongols’ ability to fight had significantly weakened. In contrast, the Vietnamese forces were brimming with energy, ready to strike back. The overconfident Mongols, having previously defeated Đại Việt, did not expect a counterattack.
On the night of January 29th, 1258, the Vietnamese extinguished their torches and, under the cover of darkness, silently sailed toward the Mongol camp. Once they approached, they suddenly lit their torches and unleashed a storm of arrows upon the Mongol guards. Then, swiftly disembarking, they launched a full-scale assault. The Mongols, caught off guard, quickly armed themselves and mounted their horses to retaliate, but it was too late. The Vietnamese had split their forces into smaller units and attacked from multiple directions, leaving the Mongols unable to regroup. Disoriented in the darkness, the Mongols suffered heavy losses.
Recognizing the situation, Uriyangqatai, the Mongol leader, ordered a retreat. The rapid withdrawal caught the Đại Việt leaders off guard, as they had not prepared to pursue the fleeing Mongols. Still, the Mongols faced attacks near Quy Hóa from Hà Bổng, a local leader, and his small force. To avoid further pursuit, the Mongols refrained from causing destruction during their retreat, leading the locals to mock them as “Buddha invaders.” A Chinese historian later remarked, “When they won, they chased their enemies relentlessly. When they lost, they fled so quickly that no one could catch them.”
After their defeat in Đại Việt, the Mongols retreated to Dali. Preoccupied with their campaign against the Song dynasty, they were unable to retaliate against Đại Việt immediately. Uriyangqatai eventually returned to China, but his forces had been reduced to less than 5,000 soldiers, down from the 50,000 they had when they first invaded.
Upon returning to the capital, Thăng Long, King Trần Thái Tông ceded the throne to Crown Prince Trần Hoảng (who became Trần Thánh Tông) on March 30, 1258. Although the war had ended, the new King remained vigilant, sending scouts to monitor the Yuan dynasty’s military movements, aware of the potential threat from the north. Together with his father, he began the process of rebuilding the economy and administrative system, which had been severely damaged by the Mongol invasion and the turmoil following the decline of the Lý dynasty.
Đại Việt diplomatic tactics after first Đại Việt – Mongols war
Not long after returning to Yunnan, the Mongols once again sent envoys to Đại Việt, this time proposing an alliance to jointly attack the Song Dynasty. However, the Trần Emperor was well aware of what had happened to the Song when they had allied with the Mongols. The Jin Dynasty had once asked the Song to help them resist the Mongols, warning that if the Mongols defeated the Jin, the Song would be their next target. The Mongols, in turn, offered the Song a deal, promising to return some land in exchange for assistance in defeating the Jin. After the Jin were conquered, however, the Mongols did not honor their agreement and instead turned their attention to invading the Song.
Outraged by the Mongols’ audacity, the Trần Emperor initially roped and expelled their envoys. But he soon realized that the Mongols were close to defeating the Song, which bordered Đại Việt. Understanding the imminent threat, the King changed his approach. When the third Mongol envoy arrived requesting tributes, he accepted their demands to maintain peace. Meanwhile, Uriyangqatai, misinterpreting this as fear, grew increasingly demanding, requesting scholars, shipbuilders, doctors, fortunetellers, and annual tributes from Đại Việt. The Vietnamese King, unwilling to comply, sent an emissary to the Mongol court to negotiate. Eventually, both sides agreed that Đại Việt would send tributes once every three years, and in return, the Mongols offered gifts.
However, soon after the Vietnamese envoy returned, yet another Mongol emissary arrived with a new demand—Uriyangqatai now required the King of Đại Việt to personally appear at the Mongol court. As the ruler of his own country, the King refused to subordinate himself in such a manner. In his reply, he subtly expressed his disapproval, writing: “A small country shows all respect to a great one, but how should a great country treat a small one?” He carefully avoided any mention of whether he would comply.
When this response reached Dali, Uriyangqatai had already left to meet Kublai Khan, and Buqa was temporarily in charge. Buqa consulted Uriyangqatai, who ordered that the demand for the Vietnamese King’s presence be repeated. The King of Đại Việt, seeking to buy time to prepare for war, responded cleverly: “I await the official command of the ‘Mandate of Heaven’ [the Mongol Emperor], after which I will send my son as a hostage,” again avoiding the question of attending the Mongol court. This response clearly indicated that the Vietnamese King had no intention of reporting to the Mongols.
Buqa, furious, reported the matter to Kublai Khan. Preoccupied with internal power struggles, Kublai Khan responded with a softer tone, sending another envoy to Đại Việt without mentioning hostages. This led to an unexpected period of peace between the two nations, as the Mongols were focused on their war with the Song. Even though Đại Việt might not have paid full tributes, the Mongols were content to avoid conflict while concentrating on their battle with the Song.
This temporary peace allowed Đại Việt valuable time to prepare for the next Mongol invasion. In 1285, after the Mongols had completed their conquest of the Song, Kublai Khan founded the Yuan Dynasty—the first and only Chinese dynasty ruled by non-Chinese. Throughout the long war between the Mongols and the Song, Đại Việt maintained friendly relations with the Song, welcoming thousands of refugees fleeing the conflict. The Trần rulers provided them with shelter, and many talented Chinese were appointed to official positions. Under the command of Prince Chiêu Văn, who had a deep understanding of Chinese language and customs, many Song refugees served in the Vietnamese military.
See also: Tran dynasty: the dynasty that defeated the Mongols 3 times
