Four major military campaigns were launched by the Mongol Empire, and later the Yuan dynasty, against the kingdom of Đại Việt (modern-day northern Vietnam) ruled by the Trần dynasty and the kingdom of Champa (modern-day central Vietnam) in 1258, 1282–1284, 1285, and 1287–1288. The campaigns are treated by a number of scholars as a success due to the establishment of tributary relations with Đại Việt despite the Mongols suffering major military defeats. In contrast, modern Vietnamese historiography regards the war as a major victory against the foreign invaders.
The first invasion began in 1258 under the united Mongol Empire, as it looked for alternative paths to invade the Song dynasty. The Mongol general Uriyangkhadai was successful in capturing the Vietnamese capital Thăng Long (modern-day Hanoi) before turning north in 1259 to invade the Song dynasty in modern-day Guangxi as part of a coordinated Mongol attack with armies attacking in Sichuan under Möngke Khan and other Mongol armies attacking in modern-day Shandong and Henan. The first invasion also established tributary relations between the Vietnamese kingdom, formerly a Song dynasty tributary state, and the Yuan dynasty. In 1283, Kublai Khan and the Yuan dynasty launched a naval invasion of Champa that also resulted in the establishment of tributary relations.
Intending to demand greater tribute and direct Yuan oversight of local affairs in Đại Việt and Champa, the Yuan launched another invasion in 1285. The second invasion of Đại Việt failed to accomplish its goals, and the Yuan launched a third invasion in 1287 with the intent of replacing the uncooperative Đại Việt ruler Trần Nhân Tông with the defected Trần prince Trần Ích Tắc. By the end of the second and third invasions, which involved both initial successes and eventual major defeats for the Mongols, both Đại Việt and Champa decided to accept the nominal supremacy of the Yuan dynasty and became tributary states to avoid further conflict.
By the 1250s, the Mongol Empire controlled large tracts of Eurasia including much of Eastern Europe, Anatolia, North China, Mongolia, Manchuria, Central Asia, Tibet and Southwest Asia. Möngke Khan (r. 1251–59) planned to attack the Song dynasty in southern China from three directions in 1259. To avoid a costly frontal assault on the Song, which would have required a risky forced crossing of the lower Yangtze, Möngke decided to establish a base of operations in southwestern China, from which a flank attack could be staged. At the Kurultai of the summer of 1252, Möngke ordered his brother Kublai to lead the southwest campaign against the Song in Sichuan. In the autumn of 1252, 100,000 Mongols advanced to the Tao River, then penetrated the Sichuan Basin, defeating a Song army and established a major base in Sichuan.
When Mongke learned that the king Duan Xingzhi of Dali in Yunnan (a kingdom ruled by the Duan dynasty) refused to negotiate and that his prime minister Gao Xiang murdered the envoys that Möngke had sent to Dali to demand the king's surrender, Möngke ordered Kublai and Uriyangkhadai to attack Dali in summer 1253.
In September 1253, Kublai launched a three-pronged attack on Dali. The western army led by Uriyangkhadai, marching from modern-day Gansu through eastern Tibet toward Dali; the eastern army led by Wang Dezhen marched south from Sichuan, and passed just west of Chengdu before reuniting briefly with Kublai's army in the town of Xichang. Kublai's army met and engaged with Dali forces along the Jinsha River. After several skirmishes in which Dali forces repeatedly turned back the Mongol raids, Kublai's army crossed the river on inflated rafts of sheepskin in the night, and routed Dali defensive positions. With Dali forces in disarray, three Mongol columns quickly captured the capital of Dali on December 15, 1253, and even though its ruler had rejected Kublai's submission order, the capital and its inhabitants were spared. Duan Xingzhi and Gao Xiang both fled, but Gao was soon captured and beheaded. Duan Xingzhi fled to Shanchan (modern-day Kunming) and continued to resist the Mongols with aid from local clans until autumn 1255 when he was finally captured.
As they had done during other invasions, the Mongols left the native dynasty in place under the supervision of Mongolian officials. Bin Yang noted that the Duan clan was recruited to assist with further invasions of the Burmese Pagan Empire and the initial successful attack on the Vietnamese kingdom of Đại Việt.
At the end of 1254, Kublai returned to Mongolia to consult with his brother about the khagan title. Uriyangkhadai was left in Yunnan, and from 1254 to 1257 he conducted campaigns against local Yi and Lolo tribes. In early 1257 he returned to Gansu and sent messengers to Mongke's court informing his sovereign that Yunnan was now firmly under Mongolian control. Pleased, the emperor honored and generously rewarded Uriyangkhadai for his fine achievement. Uriyangkhadai subsequently returned to Yunnan and began preparing for the first Mongolian incursions into Southeast Asia.
The Đại Việt kingdom, or Annam, emerged in the 960s as the Vietnamese had carved up their territories in northern Vietnam (the Red River Delta) from the local Tang remnant regime since the fall of the Tang empire in 907. The kingdom had gone through four dynasties, all of which had kept a regulated peaceful tributary relationship with the Chinese Song empire. In the autumn of 1257, Uriyangkhadai sent two envoys to the Vietnamese ruler Trần Thái Tông (known as Trần Nhật Cảnh by the Mongols) demanding submission and a passage to attack the Song from the south. Trần Thái Tông opposed the encroachment of a foreign army across his territory to attack their ally, therefore the envoys were imprisoned, and soldiers on elephants were prepared to deter the Mongol troops. After the three successive envoys were imprisoned in the capital Thang Long (modern-day Hanoi) of Đại Việt, Uriyangkhadai invaded Đại Việt with generals Trechecdu and Aju in the rear.
First invasion of Đại Việt (1258)
In early 1258, a Mongol column under Uriyangkhadai, the son of Subutai, entered Đại Việt via Yunnan. According to Vietnamese sources, the Mongol army consisted of at least 30,000 soldiers of whom at least 2,000 were Yi troops from the Dali Kingdom. Modern scholarship points to a force of several thousand Mongols, ordered by Kublai to invade with Uriyangkhadai in command, which battled with the Viet forces on 17 January 1258. Some Western sources estimated that the Mongol army consisted of about 3,000 Mongol warriors with an additional 10,000 Yi soldiers.
In the Battle of Bình Lệ Nguyên, the Vietnamese used war elephants. Trần Thái Tông even led his army from atop an elephant. Mongol general Aju ordered his troops to fire arrows at the elephants' feet. The animals turned in panic and caused disorder in the Vietnamese army, which was routed. The Vietnamese senior leaders were able to escape on pre-prepared boats, while part of their army was destroyed at No Nguyen (modern Việt Trì on the Red River). The remainder of the Đại Việt army again suffered a major defeat in a fierce battle at the Phú Lộ bridge the following day. This led the Vietnamese monarch to evacuate the capital. The Đại Việt annals reported that the evacuation was carried out "in an orderly manner"; however, this is viewed as an embellishment, because the Vietnamese had to retreat in disarray, leaving their weapons behind in the capital. According to Vietnamese historian Lê Tắc (1263-1342), the Trần army suffered 10,000 deaths in two battles against Uriyangkhadai's Mongols between January 17–22.
Trần Thái Tông fled to an offshore island, while the Mongols occupied the capital city, Thăng Long (modern-day Hanoi). They found their envoys in prison, with one of them already deceased. In revenge, Mongols massacred the city's inhabitants. Although the Mongols had successfully captured the capital, the provinces around the capital were still under Vietnamese control. While Chinese source material is sometimes misinterpreted as saying that Uriyangkhadai withdrew from Vietnam due to poor climate, Uriyangkhadai left Thang Long after nine days to invade the Song dynasty in modern-day Guangxi in a coordinated Mongol attack, with some armies attacking in Sichuan under Möngke Khan and other armies attacking in modern-day Shandong and Henan. The Mongol army gained the popular local nickname of "Buddhist enemies" because they did not loot or kill while moving north to Yunnan. After the loss of a prince and the capital, Trần Thái Tông submitted to the Mongols.