However, Tay Son rebellions broke out in 1771 and quickly occupied a large area from Quy Nhon to Binh Thuan Province, thereby weakening the authority and power of the Nguyen lords. While the war between Tây Sơn rebellion and Nguyễn lord was being fought, the Trịnh lords sent south a massive army and easily captured Phú Xuân in 1775. After the capture of Phú Xuân, the Trịnh lords' general Hoang Ngu Phuc made a tactical alliance with Tay Son and withdrew almost all troops to Tonkin and left some troops in Phu Xuan. In 1786, Tây Sơn rebellion defeated the Trịnh garrison and occupied Phú Xuân. Under the reign of emperor Quang Trung, Phú Xuân became Tây Sơn dynasty capital. In 1802, Nguyen Anh, a successor of the Nguyen lords, recaptured Phu Xuan and unified the country. Nguyen Anh rebuilt the citadel entirely and made it the Imperial City capital of all of Vietnam.