At the beginning of the 13th century, Gengis Khan, having unified Mongolia, started a war of conquest against China. In 1253, Kubilai conquered the Dai Ly kingdom (now Yunnan province), thus reaching the Vietnamese frontier. The Mongols demanded passage through Dai Viet in order to attack the Sung from the south(1257), but the Tran refused. A Mongol army invaded Dai Viet, smashed its defences, and seized the capital Thang Long, which was put to the sword and burnt to the ground. The Tran king left the capital, which was also abandoned by its inhabitants. The Mongol army were not able to obtain food and fared badly in the tropical climate. A Vietnamese counter-offensive drove tjhe Mongols out of the capital. In retreat, the enemy was attacked by local partisans from an ethnic minority group living in the Phu Tho region.
This was the first Mongol defeat.
Once they had become the overlords of China, the Mongols grew more and more demanding towards Dai Viet. Despite concession, by the Tran, the Mongol court remained intransigent, dreaming of conquering both Dai Viet and Champa. Relations between the two countries remained tense, and Mongols envoys behaved with arrogance at the Tran court. The Tran were not inactive, but rather made serious preparations for the country's defence.
In 1281, Tran Di Ai, a member of the royal family, was sent as an envoy to China. The Mongols persuaded him to accept his investiture by them as king of Dai Viet. He returned to the country with an escort of 1,000 soldiers to ascend the throne. However, the Mongol escort was beaten and he was captured.
In the meantime, the Mongols had completed preparations for an expedition by sea against Champa. At the end of 1282, a Mongol general, Toa Do (Gogetu), landed in Champa and seized its capital in 1281. But Cham resistance decimated the Mongol army. In 1284, Toa Do began withdrawing his troops, regrouping them in the northern part of Champa near the Vietnamese frontier, and awaiting further developments.
Kuhilai had been making preparations for a powerful expedition against Dai Viet and Champa; under the command of his son Thoat Hoan (Toghan), 500,000 cavalrymen and infantrymen were to rush southward to push the frontiers of the Mongol empire to the southernmost part of the Indochina peninsula.
King Tran Nhan Tong was aware of' the enemy's strategy. As early as 1282, he had assembled and consulted all the princes and high-ranking dignitaries on the action to be taken; their unanimous response was to fight. Prince Quoc Toan, only 16 years old, recruited a guard of 1,000 men to go to the front. At the close of 1283, all the princes and dignitaries were ordered to put their troops under the supreme command of Tran Hung Dao. A congress of viilage elders from all over the country was convened and the following question put to them: "Should we capitulate or fight?" A great cry rose from the assembly: "Fight!"
The Mongols demanded that their troops be allowed to pass through Dai Viet territory for the invasion of Champa. At the close of 1284, they crossed the frontier. The Vietnamese force, totalling a mere 200,000 men, was unable to withstand the first onslaught. Tran Hung Dao ordered the evacuation of the capital and was asked by the king : "The enemy is so strong that a protracted War might bring terrible destruction down upon the people. Wouldn't it be better to lay down our arms to save the population?" The general answered :"I understand Your Majesty's humane feelings perfectly, but what would become of our ancestors' land, of our forefathers' temples? If you want to surrender, please have my head cut off first". The king was rcassurcd. Hung Dao wrote a handbook on military strategy for his officers' use and issued a famous appeal which so inspired his men that they all had "Death to the Mongols!" tattooed on their arms. In the villages placards were put up enjoining the. population to resist the invader by every possible means and, if neccssary, to take refuge in the forests and mountains and continue the struggle.
In early 1285, the Mongols captured several posts, crossed the Red River and entered Thang Long. The capital was ransacked and its inhabitants massacred. General Tran Binh Trong was taken prisoner. When the enemy tried to win him over he said,: "I would rather be a ghost in the south than a prince in the north", and was subsequently executed. The Mongol gencral Toa Do left Champa to join up with the army led by his colleague O Ma Nhi (Omar). A Vietnamese army under the command of Tran Quang Khai was beaten off when it tried to block his way in Nghe An province. The Mongol fleet was sailing up the Red River. Many princes and nobles, among them LeTac and Tran Ich Tac, betrayed their country. The Tran court had to take refuge in Thanh Hoa province. The Mongols controlled the greater part of the Red River delta and Thanh Hoa and Nghe An provinces, i.e. the majority of the country's territory.
However, in the process the Mongols were forced to distribute their forces among a multitude of vulnerable posts and patrols whose task was to keep communications open. In the first months of 1285, local chiefs in the uplands inficted losses on the Mongols, while in the delta the population, leaving a vacuum before the enemy, denied them all access to supplies and put them in a most difficult position. The determination of the Tran command was thus able to be brought into full play.
From Nghe An province, Toa Do's troops, harassed by guerrillas, tried to move up the Red River and join the Mongol army stationed farther north. The Trap sent 50,000 men to intercept them, and the Mongols suffered an overwhelming defeat at Ham Tu (Hung Yen province). Fired up by this victory, Tran Hung Dao's troops dashed towards the capital. Chuong Duong, an outpost 20 km south of Thang Long, was taken. And when the Tran king with his troops left their Thanh Hoa refuge to advance toward the capital, the population rose up, harassing the rearguard of the Mongol armies. Enemy troops evacuated Thang Long and withdrew north of the Red River. The bulk of the Vietnamese forces threw themselves into battle against Toa Do's army, which was crushed at Tay Ket in July 1285; the Mongol general was killed and 50,000 of his men captured.
After posting troops along the route taken by the enemy as they retreated towards China, Hung Dao staged a frontal attack on the Mongol army. As the latter drew back, it fell into ambushes. Thoat Hoan, the Mongol commander-in-chief, escaped by hiding in a bronze cask. By August 1285, the whole country had been liberated, and the Mongol army of half a million strong defeated.
Kubilai was forced to abandon plans for an invasion of Japan in order to make preparations for a revenge expedition against Dai Viet. As the Tran princes sought to recruit new troops, General Tran Hung Dao said to them: "The strengh of an army lies in its quality, not numbers". And to the anxious king he said, "Our troops are now better trained, while the enemy, having suffered a defeat, has lost morale. Victory will be easier".
In late 1287, Thoat Hoan again crossed the frontier with 300,000 men while a Mongol fleet of 500 vessels headed for the Vietnamese coast. The Tran king again left the capital. The Mongol general O Ma Nhi sent him this warning: "Even if you fled to the sky I'd go after you. I'd pursue you to the bottom of the seas, to the heart of the forests, if necessary!" The Mongols sought to occupy more and more territory, but found only deserted areas around them. The Yuan (name of the Mongol dynasty) annals relate: "The Chiao Chih (Dai Viet) population hid their rice and fled". The invading army ran short of supplies. Thoat Hoan ordered the capital set on fire, then withdrew north of the Red River; during that time, his troops were constantly harassed by the Tran army and the population.
At Van Don on the coast (near present-day Hong Gai), General Tran Khanh Du kept a close watch on Mongol supply convoys. He caught the enemv fleet unawares, destroyed it and seized the cargoes of food. The enemy was greatly demoralized on hearing the news. The Mongols pillaged the countryside. but the population put up a heroic resistance. Thoat Hoan was told by his generals : "We have no more citadels left, no more food; the strategic passes have been lost, and summer will soon come with its retinue of diseases. We'd better withdraw". The Mongol retreat was effected by land through Lang Son and by sea, the fleet sailing down the Bach Dang River.
Tran Hung Dao used Ngo Quyen's old stratagem, iron-tipped stakes planted at the mouth of the river. General Pham Ngu Lao was sent to Lang Son to guard the mountain passes. Tran Hung Dao himself took the bulk of the troops across the Hoa River (Kien An province) and launched a big offensive. When crossing the river, Hung Dao publicly swore the following oath : "If the Mongols are not defeated, we will not recross this river".
At high tide, the Mongol fleet sailing down the Bach Dang was engaged by a small Vietnamese fleet which soon retreated. O Ma Nhi's forces were pursuing it when Tran Hung Dao's army turned up. The Mongol fleet beat a hasty retreat, but by this time the tide was ebbing and the Mongol junks broke up on the irontipped stakes. O Ma Nhi was taken prisoner and 100 of his junks were destroyed and another 400 captured (April 3, 1228).
Thoat Hoan was terrified on learning the news, and hurriedly withdrew. His troops were decimated during their retreat, the third Mongol defeat. In late 1288, the Tran king wisely sent a mission to China to negotiate, offering tribute to the Mongol court. In 1289, he handed over the captured Mongol generals and officers. The Chinese court wanted more than this formal recognition of suzerainty but its demands were not accepted. In 1293, the Mongols began organizing another expedition but Kubilai died in 1294 and his son Timour abandoned the project. The new ruler established friendly relations with Dai Viet, which continued to pay tribute annually to the Mongol court.
The principal reason for the victory over the Mongols was the strength of the socioeconomic system established under the Ly and Tran, and the successful military policy followed by the Tran command. The monarchy and nobles had promoted the development of agriculture and instituted a peasant-soldier system so that when a war occurred, the whole nation united around its chiefs, each man becoming a combatant. Ethnic minority chieftains in mountainous regions also contributed to victory. National unity became a reality. National consciousness, moulded over the course of many centuries of struggle against foreign aggressors and consolidated by the establishment of stable centralized power had been considerably strengthened. General Tran Hung Dao never failed to seek the support of the population in his fight against an enemy superior in numbers and armaments, and he used appropriate strategies and tactics. He willingly left towns, and even the capital where necessary, avoided combat when the enemy was too strong, resorted to guerrilla harassment, and resolutely took the offensive whenever the circumstances were favorable. The fierce determination of his command galvanized the men.
On a visit to Tran Hung Dao shortly before died in 1300, King Tran Anh Tong asked him, "What should we do in the event of a new invasion from the north?" Hung Dao replied, "The enemy relies on numbers. To oppose the long with the short - therein lies our skill. If the enemy makes a violent rush forward, like fire and tempest, it is easy to defeat him. But if he shows patience, like the silkworm nibbling at the mulberry leaf, if he proceeds without haste, refrains from pillaging, and does not seek a quick victory, then we must choose the best generals and effective tactics, as in a chess game, The army must be united and of one mind, like father and son. It is essential to treat the people with humanity, so as to strike deep roots and ensure a lasting base". Ever since then, the memory of Tran Hung Dao has been honored at the Kiep Bac temple