The Trịnh lords, who ruled the northern half of the country, sent a large army to attack in 1775, which forced Nguyen king Nguyễn Phúc Thuần to flee to Quảng Nam.
The Tay Son army was defeated by Trinh lord in Cẩm Sa (a place in mordern Hòa Vang District, Quảng Nam).
Nguyễn Nhạc had to be reconciled with Trinh, and directed their fire at Nguyen lord, forcing Thuần to flee to Long Xuyên.
Nguyễn Phúc Dương escaped and fled to Gia Dinh (mordern-day Ho Chi Minh City) in 1776, Lý Tài betrayed Tay Son army in the same time.
Lý Tài came into conflict with another important general Đỗ Thanh Nhơn, forced him to flee to Vĩnh Long (in mordern-day Bến Tre).