What happened
The Mongols invaded Đại Việt in 1258 and, under Kublai Khan’s Yuan dynasty, again in 1285 and 1287–88; the chronicles put the later armies in the hundreds of thousands, figures that rest on those sources. Each time the Trần court abandoned the capital Thăng Long, scorched the earth, and wore the invaders down with guerrilla war, heat, and disease before counterattacking — under the supreme command of Trần Hưng Đạo in the later invasions.
The finale came on the Bạch Đằng River in 1288, where Trần Hưng Đạo reused Ngô Quyền’s stratagem of 938: the Yuan fleet was impaled on hidden stakes and destroyed, and its admiral Omar (O Ma Nhi) was captured.
Background
The Yuan sought passage and submission from Đại Việt, which lay on the route of its campaigns against Champa and the remnants of the Song.
Consequences
Đại Việt preserved its independence while resuming nominal tribute to the Yuan court. The victories became foundation stones of Vietnamese national memory.