Mongol invasions of Vietnam

Mongol invasions of Vietnam or Mongol-Vietnamese War refer to the three times that the Mongol Empire and its chief khanate the Yuan Dynasty invaded Dai Viet ( now northern Vietnam) during the Tran Dynasty and the Kingdom of Champa: in 1257–1258, 1284–1285, and 1287–1288.

Background
By 1250, the Mongol Empire controlled most of Eurasia including Eastern Europe, North China, Central Asia, Manchuria, Turkey, Tibet and Iran. At the same time the Koreans revolted against the rule of the Great Khan of the Mongol Empire though the Goryeo court accepted the demand of submission.

Möngke Khan (r. 1251–59) planned to attack Song China from three directions in 1259. Therefore, he ordered the prince Kublai (Khubilai) to pacify the Dali Kingdom. After subjugating Dali, Kublai sent one column under Uriyangkhadai to the south-east. Uriyangkhadai sent envoys to demand the submission of Đại Việt, but the Tran Vietnamese imprisoned the Mongol envoys. This action led Uriyangkhadai and his son Aju to invade Đại Việt with 40,000 Mongols and 10,000 Yi tribesmen.

The First Mongolian Invasion 1257- 1258 A.D
In 1257, a Mongol column under Uriyangkhadai, the son of Subutai, invaded Đại Việt. A battle was fought in which the Vietnamese used war elephants. 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 King of Vietnam fled to an offshore island, and the Mongols occupied the capital city. When they found their envoys in prison, one of whom died, they responded by massacring the population of the capital. The King of Đại Việt agreed to submit.

The following year (1259), Uriyangkhadai returned to Đại Việt with an army of three thousand Mongols and ten thousand local troops from the conquered Kingdom of Dali, now the Yuan province of Yunnan. He led this army into Song China, and fought his way to the Yangtze River, joining with an army led by Kublai which had invaded from the north and was besieging Ezhou (modern Wuhan).

The Vietnamese had submitted unwillingly, and were reluctant vassals. The King repeatedly ignored demands to attend the Yuan court and offer his personal submission to the Great Khan. Nevertheless, according to the history of the Yuan Dynasty, the Trần court sent tribute every three years and received a darughachi. By 1266, however, a standoff developed, as the King Thánh Tông sought a loose tributary relationship, while Kublai demanded full submission. Thánh Tông sent an official letter requiring Kublai to take his darughachi back. Because of civil war in the Mongol Empire, and the Yuan conquest of Song China, armed conflict was delayed. Instead, Kublai reminded him of the peace treaty signed by the Mongols and Đại Việt.

As a result of the Mongol conquest of the Song Empire, by 1278–79, Mongol troops reached Đại Việt's northern borders. Some former Song officials fled to Annam and Champa, former vassals of Song China, during the final stage of Mongolian conquest of China. The Trầns' new ruler Nhân Tông resisted renewed Mongol demands for personal attendance at Kublai's court, but dispatched his uncle Tran Di Ai as envoy. Kublai tried to enthrone Di Ai as prince in 1281 but Di Ai and his small army were ambushed by Đại Việt forces.

Champa
Sogetu of the Jalayir, the governor of Canton, was dispatched to demand the submission of Champa. Although, the king of Champa accepted the status of a Mongol protectorate, his submission was unwilling. In 1282, Sogetu led a maritime invasion of Champa with 5,000 men, but could only muster 100 ships because most of the Yuan dynasty's ships had been lost in the invasions of Japan. However, Sogetu was successful in capturing Vijaya, the Champa capital later that year. The aged Champa king Indravarman V retreated out of the capital, avoiding Mongol attempts to capture him in the hills. His son would wage a guerrilla war with the Mongols for the next few years, eventually wearing down the invaders. Stymied by the withdrawal of the Champa king, Sogetu asked reinforcements from Kublai but sailed home in 1284, just as another Mongol fleet with more than 15,000 troops under Ataqai and Arigh Khaiya reembarked on a fruitless mission to reinforce him. Sogetu presented his plan to have more troops invade Champa through Đại Việt. Kublai accepted his plan and put his son Toghan in command, with Sogetu as second in command.

The Second Mongolian Invasion, 1284-85 A.D.
In 1284 Kublai appointed his son Toghan (tiếng Việt: Thoát Hoan) to conquer Champa. Toghan demanded from the Tran a route to Champa, which would trap the Champan army from both north and south. While Nhân Tông preferred to accept the demand, General Hưng Đạo rallied 15,000 troops and refused to help the Mongols by providing a route and supplies. However, Toghan defeated Hung Dao's army and reoccupied Thăng Long in June, 1285. Drawing from experience with previous Chinese invasions, the Đại Việt royal family abandoned the capital, and retreated south, while enacting a scorched earth campaign by burning villages and crops. At the same time, Sogetu moved his army up north in an attempt to envelop Đại Việt in a pincer movement. The Cham were in hot pursuit of Sogetu, however, and managed to kill Sogetu and defeat his army while it was moving north. As the Yuan forces advanced down the Red River, dispersing their power, General Quang Khải counterattacked them at Chương Dương, forcing Toghan to withdraw. Toghan returned without a huge loss of the army under him thanks to the Kypchak officer Sidor and his navy. Seeing the Mongol force weakened under the Vietnamese heat and sickness, Trần Hưng Đạo took this opportunity to strike, selecting battlefields where the Mongol cavalry could not be fully employed. The Mongol forces under Sogetu and Li Heng (tiếng Việt: Lí Hằng) suffered a major defeat on the muddy grounds of the Red River. The Yuan army retreated north, but few made it back to China due to pursuing Đại Việt troops and fighters from the Hmong and Yao peoples.

The next year Kublai installed Nhân Tông's younger brother Trần Ích Tắc, a defector to the Yuan, as prince of Đại Việt, but hardship in the Yuan's Hunan supply base aborted his plan.

The Final Mongolian Invasion, 1287–1288 A.D.
In 1287 Toghan invaded with 70,000 regular troops, 21,000 tribal auxiliaries from Yunnan and Hainan, a 1,000-man vanguard under Abachi, and 500 ships under the Muslim Omar (tiếng Việt: Ô Mã Nhi) and Chinese Fanji (according to some sources, the Mongol force was composed of 300,000–500,000 men). Kublai sent veterans such as Arigh Khaiya, Nasir al-Din and his grandson Esen-Temür. The strategy of this invasion was different: a huge base was to be established just inland from Hải Phòng, and a large-scale naval assault mounted as well as a land attack. Trần Hưng Đạo withdrew from inhabited areas, leaving the Mongols with nothing to conquer. 500 vessels were prepared to bring provisions to Toghan's army. Borrowing a tactic used by general, later Emperor Ngô Quyền in 938 to defeat an invading Chinese fleet, the Đại Việt forces drove iron-tipped stakes into the bed of the Bạch Đằng River, and then, with a small flotilla, lured the Mongol fleet into the river just as the tide was starting to ebb, while their route to the sea had been blockaded by large warships. Unable to return or escape to the sea, the entire Mongol fleet of 400 craft was caught in a bloody boarding and missile battle, sunk, captured, or burned by fire arrows. This would later become known as the Battle of Bạch Đằng. Caught between the Champa and Đại Việt, Sogetu lost his life. The Mongol army retreated to China, harassed en route by Trần Hưng Đạo's troops. The Yuan officers such as Abachi and Fanji died in bloody retreat and Omar was captured.

Aftermath in Đại Việt
Kublai angrily banished Toghan to Yangzhou for life. The Mongols and the Tran Vietnamese agreed to exchange their war prisoners. While Nhan Tong was willing to pay tribute to the Yuan, relations again foundered on the question of attendance at the Mongol court and hostile relations continued.

The Trần Dynasty decided to accept Mongol supremacy in order to avoid further conflicts. Because he refused to come in person, Kublai detained his envoy, Dao-tu Ki, in 1293. Kublai's successor Temür Khan (r.1294-1307), finally released all detained envoys, settling for a tributary relationship, which continued to the end of the Mongol Empire.

Aftermath in Champa
The Champa Kingdom decided to accept Mongol supremacy. A tributary relationship continued for some time, but Champa disappears from Yuan records before 1300. The king of Champa made the act of vassalage to the Mongols.