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The Mongol Invasions of Vietnam
The Mongols Enter Southeast Asia
In 1253 AD the Mongol Empire, among the largest and most militarily successful states in history, entered Southeast Asia through the conquest of the kingdom of Nanzhao (in modern Yunnan). This was all part of Mongol grand strategy, as the annexation of Nanzhao provided the Mongols with the means to outflank their stubborn Chinese opponents. Kublai Khan would later see Southeast Asia as the key to his ambitions for maritime empire and control of the Indian Ocean trade.
In 1257 the Mongols made their formal introduction to the kingdoms of modern Vietnam when Uryankhadai and his son Aju led an invasion force through the area as part of an assault upon the Song. Northern Vietnam at this time was ruled by the weak kingdom of Dai Viet (called Annam by the Chinese). Central and southern Vietnam was ruled by Champa, a non-Vietnamese kingdom heavily influenced by Indian culture. The king of Dai Viet had refused to allow the Mongols to attack through his lands, causing them to adjust their strategy.
The First Invasion
Uryankhadai, marching out of Yunnan, at first met little resistance. Mongol cavalry easily achieved dominance in the flat areas of central Dai Viet, and surrounded Thang Long, the capital (modern Hanoi). Tran Thai Tong, the king, was called on to surrender. He refused and fled with his court out to sea, taking refuge on an island out of Mongol reach. Thang Long fell after a short siege in 1258, the Mongols massacring the population when they discovered one their envoys had been executed by the king. Nine days later, during the summer, they retreated back to safety. A combination of lack of sufficient manpower to hold the capital, attacks on their supply lines, and the unhospitable climate had forced the Mongol retreat.
Vietnam, with a view of Yunnan and Guangxi
Interlude and the Invasion of Champa
Tran Thai Tong returned to his capital once the Mongol retreat was confirmed. He then released the remaining Mongol envoys he held hostage and abdicated in favor his heir. Tran Thanh Tong embarked on a program of national self-strengthening, paying tribute to Kublai Khan after he came to power in 1260 to buy time. Unfortunately for the Vietnamese, the Mongols only became more powerful under the new khan’s leadership, resulting in the foundation of the Yuan dynasty in 1271 and the fall of the Southern Song five years later. By the abdication of Thanh Tong in 1278 the Yuan were Dai Viet’s only northern neighbor and exerting pressure from across the border. Promises to not aid the Song remnants were extracted from both Thanh Tong and his successor Nhan Tong. However, the successful defiance of the Kamakura Bakufu of Japan (1274 and 1281) and the Burmese Kingdom of Bagan (1277) broke the myth of Mongol invincibility, encouraging the Vietnamese. In 1281 Kublai made a Tran royal uncle heading a diplomatic party “King of Annam” and sent him back to Thang Long with an armed escort and their own envoys. The court allowed the Yuan envoys through, but arrested the errant uncle and nothing came of the attempted coup except more frustration for the khan.
In 1282, Kublai Khan demanded personal tribute and submission from Champa. The khan was convinced Champa was the lynchpin of the Indian Ocean trade and desired to control it. To ease the sending of reinforcements and supplies he demanded the use of Dai Viet territory as a base for his forces heading south. The Vietnamese stalled, keeping the Yuan diplomats occupied by endless talking. Meanwhile, the elderly Indravarman V refused to submit and fled to the mountains. The Crown Prince, Che Man, took charge of the defense. Later in the year Yuan forces under Sogetu, a leading marshal, landed at the capital of Vijaya (also called Chamapura) and occupied it. Che Man then surprised them with a fierce guerrilla war. The Chams burned their own villages and forced the Mongols to fight on unfavorable terrain, harrying the invaders through the heavy use of crossbow cavalry and of siege crossbows mounted on elephants. The marshal now found himself caught in a quagmire: On one side he was faced with guerrilla fighters. On the other a city he could not fully control, in terrain hostile to his forces. The invasion bogged down. In the spring of 1284 Sogetu abandoned his camp on the coast close to the capital and sailed for northern Champa, finding better luck in battle there and taking the opportunity to gather supplies and ask for reinforcements. Later that year, however, instead of the expected reinforcements Sogetu was ordered force for a new invasion of Dai Viet.
The Second Invasion
The first real invasion of Dai Viet was undertaken in late 1284-early 1285. Hoping that a quick strike would eliminate Tran resistance Kublai had sent two armies south (supposedly totaling 300,000 men) under the overall command of his son Prince Togan. Taking advantage of their conquest of the Song, the invading armies marched south from Guangxi as well as Yunnan. A flotilla of warships was also accompanying the Yuan troops. The Vietnamese, under the command of a royal prince named Tran Quoc Tuan (better known as Tran Hung Dao), tried to prevent the Yuan forces from linking but failed and Thang Long fell a month into the invasion. Before long Dai Viet looked to be in danger of being crushed between Togan and Sogetu, arriving from the south. Mass defections followed. Quoc Tuan struck back with the onset of the summer rains, defeating the Yuan at modern Hung Yen and making hard for Thang Long. A series of running battles ended in Togan abandoning the capital, withdrawing to his supply depot at modern Van Kiep. The other armies fared no better, harried endlessly.
The Vietnamese played to their strengths, refusing to engage the Yuan, and especially the Mongol cavalry, on flat ground but only across rivers and streams. Ambushes were preferred to set battles and this, combined with a policy of scorched earth and the climate, forced the invaders to retreat into China. Sogetu and the Yuan naval forces were defeated separately at the battle of Tay Ket and the marshal was captured and killed. The war has lasted six months, the Mongols had been beaten back.
The Third Invasion and the Battle of Bach Dang
But Kublai refused to accept this. Now more obsessed with Vietnam than anything else, the khan put on hold plans for a third invasion of Japan to conquer Dai Viet and Chamly. In 1287 Yuan armies re-entered Dai Viet. Togan linked with his other columns as before but lost his supply fleet at Van Don before the campaign could even begin. Thang Long fell for the third time and the Dai Viet armies retreated down the Red River. But low supplies forced the invaders to return to Thang Long while their navy searched for the supply fleet. A month later they met up again at Van Kiep, soon surrounded by the resurgent Vietnamese. After another month had passed the Yuan forces broke out, dangerously low on food, and retreated.
But Tran Quoc Tuan was not willing to allow them all to leave. At the estuary of the Bach Dang River, near modern Haiphong, he saw his chance. Hoping to repeat the success of Ngo Quyen against the Southern Han in 939, Quoc Tuan had his men line the bed of the river with short wooden poles topped with iron points. He then sent his numerically inferior navy to lure the Yuan warships into the river mouth at high tide. When the tide receded the ships became stuck and the Dai Viet forces swarmed over them, wiping out the Yuan naval forces and capturing their admiral, Omar. Togan retreated in disgrace and the Mongols would not return. Dai Viet and Champa would both resume sending tribute to Dadu, the Yuan capital, but from a position of strength instead of weakness.