Trần dynasty
Peace and southward expansion

After the Mongol invasions, king Trần Nhân Tông led an attack into modern-day Laos in the winter of 1289–1290 against the advice of his advisors with the goal of preventing raids from the inhabitants of the highlands. Famines and starvations ravaged the country from 1290 to 1292. There were no records of what caused the crop failures, but possible factors included neglect of the water control system due to the war, the mobilization of men away from the rice fields, and floods or drought.

There was a relatively long period of prosperity and peace during the reigns of Trần Anh Tông, Trần Minh Tông, and Trần Hiến Tông. Anh Tông was the first Trần emperor to reign without facing attacks from the Mongol Empire. Despite the deaths of the two most important generals of the early Trần dynasty, Trần Quang Khải in 1294 and Trần Quốc Tuấn in 1300, the Emperor was still served by many efficient mandarins like Trần Nhật Duật, Đoàn Nhữ Hài, Phạm Ngũ Lão, Trương Hán Siêu, Mạc Đĩnh Chi, and Nguyễn Trung Ngạn. Anh Tông was very strict in suppressing gambling and corruption, but he also generously rewarded those who served him well.

In 1306, the king of Champa, Chế Mân, offered Vietnam two Cham prefectures, Ô and Lý, in exchange for a marriage with the Vietnamese princess Huyền Trân. Anh Tông accepted this offer, then took and renamed Ô prefecture and Lý prefecture as Thuận prefecture and Hóa prefecture. These two prefectures soon began to be referred to collectively as the Thuận Hóa region. Only one year into the marriage, Chế Mân died and, in line with the royal tradition of Champa, Huyền Trân was to be cremated with her husband. Facing this urgent condition, Anh Tông sent his mandarin Trần Khắc Chung to Champa to save Huyền Trân from an imminent death.

Finally Huyền Trân was able to return to Đại Việt, but Chế Chí, the successor of Chế Mân, no longer wished to abide by the peace treaty with Đại Việt. After that event, Anh Tông himself, along with the generals Trần Quốc Chân and Trần Khánh Dư, commanded three groups of Đại Việt military units to attack Champa in 1312. Chế Chí was defeated and captured in this invasion, and Anh Tông installed a hand-picked successor, but the relations between Đại Việt and Champa remained strained for a long time afterwards.
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