Teacher:Answer the question from the given passage. Your answer should be directly extracted from the passage, and it should be a single entity, name, or number, not a sentence.
Teacher: Now, understand the problem? Solve this instance: Passage: Kublai's government faced financial difficulties after 1279. Wars and construction projects had drained the Mongol treasury. Efforts to raise and collect tax revenues were plagued by corruption and political scandals. Mishandled military expeditions followed the financial problems. Kublai's second invasion of Japan in 1281 failed because of an inauspicious typhoon. Kublai botched his campaigns against Annam, Champa, and Java, but won a Pyrrhic victory against Burma. The expeditions were hampered by disease, an inhospitable climate, and a tropical terrain unsuitable for the mounted warfare of the Mongols. The Tran dynasty which ruled Annam (Dai Viet) crushed and defeated the Mongols at the Battle of Bạch Đằng (1288). The Chinese region of Fujian was the original home of the Chinese Tran (Chen) clan before they migrated under Trần Kinh (陳京, Chén Jīng) to Dai Viet and whose descendants established the Trần dynasty which ruled Vietnam Đại Việt, and certain members of the clan could still speak Chinese such as when a Yuan dynasty envoy had a meeting with the Chinese-speaking Trần prince Trần Quốc Tuấn (later King Trần Hưng Đạo) in 1282. Professor Liam Kelley noted that people from Song dynasty China like Zhao Zhong and Xu Zongdao fled to Tran dynasty ruled Vietnam after the Mongol invasion of the Song and they helped the Tran fight against the Mongol invasion. The Tran dynasty originated from the Fujian region of China as did the Daoist cleric Xu Zongdao who recorded the Mongol invasion and referred to them as 'Northern bandits'. Annam, Burma, and Champa recognized Mongol hegemony and established tributary relations with the Yuan dynasty. Question: When were the Mongols defeated by the Tran?
Student:
1288