The Tây Sons will spend the 1780s consolidating their control over the former Nguyen territory.

Nguyen Ánh proves to be a stubborn enemy, having convinced the King of Siam, P'ya Taksin, to invade Vietnam in support of him.

The Siamese army attacks in 1780, but in several years of warfare is unable to defeat the Tây Son army, as gains are followed by losses.

The Siamese king is killed in 1782 in a revolt, and Nguyen Ánh's forces are driven out of Vietnam less than a year later.

Nguyen Huệ, having vanquished the Nguyen for the time being, decides to destroy the power of the Trịnh.

He marches north at the head of a large army in 1786, and after a short campaign, defeats the Trịnh army.

The Trịnh are also unpopular and the Tây Son army seems invincible.

The Trịnh clan flees north into China.

Huệ marries Lê Ngọc Hân, the daughter of the nominal Lê Emperor, Lê Hiển Tông.

The Lê Emperor, realizing that his hope of retaining power has gone, flees north a few months later to the Qing Empire, where he formally petitions the Qianlong Emperor for aid.

Qianlong agrees to restore Lê Chiêu Thống to power, and in 1788, a large Qing army marches south into Vietnam and captures the capital Thăng Long (present Hanoi).

Nguyen Huệ gathers a new army and prepares to fight the Qing army.

He addresses his troops before the battle saying: “The Qing have invaded our country and occupied the capital city, Thăng Long. In our history, the Trưng Sisters fought against the Han, Đinh Tiên Hoàng against the Song, Trần Hưng Đạo against the Mongol Yuan, and Lê Lợi against the Ming. These heroes did not resign themselves to standing by and seeing the invaders plunder our country; they inspired the people to fight for a just cause and drive out the aggressors... The Qing, forgetting what happened to the Song, Yuan and Ming, have invaded our country. We are going to drive them out of our territory.”

Nguyễn Huệ's army defeats the Qing in a surprise attack at the Battle of Đống Đa while the army is celebrating the Lunar New Year, and forces them, along with Lê Chiêu Thống, to flee to Qing-controlled China.

Nguyen Huệ has won the battle, but eventually submits himself as a vassal of the Qing Empire and agrees to pay annual tribute.