Nguyễn Nhạc (Vietnamese: [ŋwĩəŋ ɲâːk̚] chữ Hán: 阮岳, born 1743, died 1793) was the founder of the Tây Sơn dynasty, reigning from 1778 to 1788.

From 1778 to 1788, Nguyễn Nhạc proclaimed himself Emperor Thái Đức (Vietnamese: [tʰǎːj ɗɨ́k̚] chữ Hán: 泰德).

Hiến encouraged Nhạc to revolt against Nguyễn lords: "The prophecy says: 'Revolt in the West, success in the North'.

One day, Nhạc sat in a prison van, ordered his men to take him to Quy Nhơn.

Nguyễn lord sent his main forces to Quảng Nam, but failed to drive the rebels out of this province.

Several months later, Tây Sơn army took Quảng Nam, Thuần had to flee to Gia Định.

Tập Đình was raided by Trịnh cavalry and ultimately led to Tây Sơn's defeat.

In the letter, Nhạc said he decided to swear allegiance to the crown prince Dương, and prepared to resume the capital Phú Xuân.

[2] Trịnh army marched to Quảng Ngãi, but most of soldiers died from disease, Hoàng Ngũ Phúc had to retreat.

Phúc died of illness on his way back to Phú Xuân; his assistant, Bùi Thế Đạt, was appointed as the successor.

[6] Quảng Nam was reoccupied by Tây Sơn army; now, Nhạc could concentrate on fighting against Nguyễn lord.

Nguyễn Phúc Dương was imprisoned in a Buddhist temple; later, he fled to Gia Định, there he was supported by Lý Tài and ascended the lord throne.

In 1778, Nhạc crowned the emperor, and changed era name to "Thái Đức" (泰德), marking the establishment of Tây Sơn dynasty.

[2] A nephew of Thuần, Nguyễn Ánh, managed to escape to Hà Tiên[7]: 520  then to Poulo Panjang.

[8]: 423 [9]: 234  In late 1777, the main part of the Tây Sơn army left Saigon and marched north.

Đỗ Thanh Nhơn, the leader of Đông Sơn army, also swore allegiance to Ánh.

Huệ took his advice, marched further north without Nguyễn Nhạc's order, and finally captured Thăng Long.

Nguyễn Nhạc proclaimed himself as Trung ương Hoàng đế (中央皇帝 "the Central Emperor").

Nguyễn Lữ was given the title Đông Định vương (東定王 "King of Eastern Conquering"), Gia Định was his fief; Nguyễn Huệ received the title Bắc Bình Vương (北平王 "King of Northern Conquering") and lived in Phú Xuân, the area north to Hải Vân was his fief.

The main forces of Gia Định was called back to support Nhạc, but was defeated in Phú Yên, its commander Đặng Văn Chân surrendered to Huệ.

Nhạc climbed onto the city wall, and shouted to Huệ: "How can you use the pot of skin to cook meat like that?".

[note 3] It is an old custom, if hunters seized a prey in the jungle without a pot, they would flay it and use its skin to cook meat.

Huệ proclaimed himself as Emperor Quang Trung in 1788, and defeated Qing army in Battle of Ngọc Hồi-Đống Đa.

Meanwhile, the civil war of Tây Sơn brothers had provided Nguyễn Ánh with the chance to go back to Cochinchina again.

During his final years, he only controlled three provinces: Quy Nhơn (modern Bình Định), Quảng Ngãi and Phú Yên.