The Nguyen, at last recognizing the serious scale of the revolt, make peace with the Siamese, giving up some land they had conquered in previous decades.

However, their problems are compounded when Trịnh Sam chooses to end the one hundred-year peace and exploit the turmoil in the south by sending his army to attack Phú Xuân (modern day Huế), the Nguyen capital.

The Trịnh army captures the city, forcing the Nguyen to flee to Gia Định (later called Saigon).

The Trịnh army continues to head south and the Tay Son army continues its conquest of other southern cities.

The Nguyen are unpopular at this time, and the forces against them are too powerful.

The Tay Son army captures Gia Định, the last Nguyen stronghold, in 1776, and massacres the town's Han Chinese population.

The entire Nguyen family is killed at the end of the siege, except for one nephew, Nguyen Ánh, who manages to escape to Siam.

While they say they want to restore power to the Lê, one of the brothers, Nguyen Nhạc, proclaims himself Emperor in 1778.

A conflict with the Trịnh is thus unavoidable.