In 1786, the Tay Son troops headed North to overthrow the Trinh Lords. on 21st July 1786, Thang Long was controlled by the Tay Son troops. The 241-year rule of the Trinh Lords (1545-1786) in the North (194-year rule in Thang Long) and the two-century partition of the country between Dang Trong and Dang Ngoai came to an end.
Nguyen Hue, the Commander-in-Chief of Tay Son army, graciously returned power to the Le King. In return, the King gave him the hand of his daughter, Princess Le Ngoc Han.
Thereafter, Nguyen Hue returned to the South. King Le Chieu Thong could not govern the country, and an acute scramble for power arose among several militant groups. The Tay Son troops had to go to the North against to calm down the unrest led by Nguyen Hue himself. During one month’s staying in Thang Long, Nguyen Hue managed to attract many progressive intellectuals and also reorganized the government in the North.
By the end of 1788, the country, Thang Long included, faced a large-scale aggression launched by the Qing Dynasty from China. Under the pretext of responding to a request for assistance from King Le Chieu Thong, the Qing sent a 290,000-strong army to Vietnam in an attempt to conquer it.
The news reached Phu Xuan (present-day Hue), and Nguyen Hue ascended the throne as Emperor Quang Trung on 22nd December 1788. He immediately set out for the North with his army and quickly reached Tam Diep (in between Thanh Hoa and Ninh Binh Provinces) by 15th January 1789. Then, during the eve of the Lunar New Year’s Day of that year (25th January 1789), the Tay Son forces left Tam Diep and started his series of attacks. In the morning of the fifth of the first lunar month (30th January 1789), his troops simultaneously attacked two outposts in Ngoc Hoi and Dong Da. By noon of the same day, the enemy’s positions were smashed. The enemy troops retreated towards China in panic with its General leaving behind his own seal. At present, a festival is held every year at the Dong Da hill to celebrate this victory.
During the Tay Son Dynasty, Phu Xuan was the country’s capital, where Quang Trung reigned, while Thang Long was the chief city in the North. However, the Royal Citadel in Thang Long was well maintained and repaired. King Quang Trung issued policies to encourage agriculture, handicrafts and trade which brought in remarkable fruits in Thang Long.
The Tay Son Dynasty did not last long but left vivid marks on the historical pages of Thang Long-Hanoi.