Tây Sơn Dynasty The name of Tây Sơn is used in various ways to refer to the period of peasant rebellions and decentralized dynasties established between the end of the figurehead Later Lê dynasty and beginning of the Nguyễn dynasties in the history of Vietnam between 1770 and 1802 . Some academics refer to this period as the " Tây Sơn uprising . " The name is used to refer to the leaders of this revolt ( the Tây Sơn brothers ) , their uprising ( the Tây Sơn Uprising ) or their rule ( the Tây Sơn Dynasty or Nguyễn Tây Sơn Dynasty ) . Background . During the 18th century , Vietnam was under the nominal rule of the officially revered , but politically powerless Lê Dynasty . Real power was in the hands of two warring feudal families , the Trịnh Lords of the north who controlled and ruled from the imperial court in Hanoi and the Nguyễn Lords in the south , who ruled from their capital Huế . Both sides fought each other for control of the nation , while claiming to be loyal to the king . Life for the peasant farmers was difficult . Ownership of land became more concentrated in the hands of a few landlords as time passed . The Mandarin bureaucracy was oppressive and often corrupt ; at one point , royal - sanctioned degrees were up for sale for whoever was wealthy enough to purchase them . In contrast to the people , the ruling lords lived lavish lifestyles in huge palaces . The decades - long war between the Trịnh and the Nguyễn had ended in 1673 , and life for the northern peasants was fairly peaceful . However , the Nguyễn Lords engaged in a regular series of wars with the weak Khmer Empire , and later , the fairly strong state of Siam . While the Nguyễn usually won , and despite the fact that the new lands they conquered offered new opportunities for the landless poor , the frequent wars took a toll on their popularity . Conquest of the Nguyễn . In 1769 , the new king of Siam , King Taksin , launched a war to regain control of Cambodia . The war generally went against the Nguyễn and they were forced to abandon some of the newly conquered lands . This failure , coupled with heavy taxes and corruption at the local level , caused three brothers from the village of Tây Sơn to begin a revolt against Lord Nguyễn Phúc Thuần . The Tây Sơn brothers styled themselves as champions of the people . Over the next year , the revolt gained traction and they won some battles against the Nguyễn army units sent to crush their rebellion . The Tây Sơn had a great deal of popular support , not only from the poor farmers , but from some of the indigenous highland tribes . The leader of the three brothers , Nguyễn Huệ , was also a very skilled military leader . Nguyễn Huệ said that his goal was to end the people ' s oppression , reunite the country , and restore the power of the Lê emperor in Hanoi . The Tây Sơn also promised to remove corrupt officials and redistibute land . In 1773 the Tây Sơn captured the port of Qui Nhơn , where the merchants , who had suffered under restrictive laws put in place by the Nguyễn , gave the uprising financial support . The Nguyễn , at last recognizing the serious scale of the revolt , made peace with the Siamese , giving up some land they had conquered in previous decades . However , their problems were compounded when Trịnh Sâm chose to end the 100 - year peace and exploit the turmoil in the south by sending his army to attack Phú Xuân ( modern day Huế ) , the Nguyễn capital . The Trịnh army captured the city , forcing the Nguyễn to flee to Gia Định ( later called Saigon ) . The Trịnh army continued to head south and the Tây Sơn army continued its conquest of other southern cities . The Nguyễn were unpopular at this time , and the forces against them were too powerful . In 1776 , the Tây Sơn army captured the last Nguyễn stronghold of Gia Định and massacred the town ' s Han Chinese population . The entire Nguyễn family was killed at the end of the siege , except for one nephew , Nguyễn Ánh , who managed to escape to Siam . While they said they wanted to restore power to the Lê , one of the brothers , Nguyễn Nhạc , proclaimed himself Emperor in 1778 . A conflict with the Trịnh was thus unavoidable . Conquest of the Trịnh . The Tây Sơn spent the next decade consolidating their control over the former Nguyễn territory . Nguyễn Ánh proved to be a stubborn enemy . He convinced the King of Siam , P ' ya Taksin , to invade Vietnam in support of him . The Siamese army attacked in 1780 , but in several years of warfare , it was unable to defeat the Tây Sơn army , as gains were followed by losses . In 1782 , the Siamese king was killed in a revolt , and less than a year later , Nguyễn Ánh ' s forces were driven out of Vietnam . Having vanquished the Nguyễn for the time being , Nguyễn Huệ decided to destroy the power of the Trịnh . He marched north at the head of a large army in 1786 , and after a short campaign , defeated the Trịnh army . The Trịnh were also unpopular and the Tây Sơn army seemed invincible . The Trịnh clan fled north into China . Huệ married Lê Ngọc Hân , the daughter of the nominal Lê Emperor , Lê Hiển Tông . Defeat of Manchu Qing . A few months later , realising that his hope of retaining power had gone , the Lê Emperor fled north to the Qing Empire , where he formally petitioned the Qing Emperor Qianlong ( Vietnamese : " Càn Long " ) for aid . Qianlong agreed to restore Lê Chiêu Thống to power , and so in 1788 , a large Qing army marched south into Vietnam and captured the capital Thăng Long . Nguyễn Huệ gathered a new army and prepared to fight the Qing army . He addressed his troops before the battle saying : In a surprise attack , while the Qing army was celebrating the Lunar New Year , Nguyễn Huệ ' s army defeated them at the Battle of Đống Đa and forced them , along with Lê Chiêu Thống , to flee to the Qing - controlled China . Nguyễn Huệ and his army chased the defeated army of the Qing over the China borders and captured many provinces of the Qing . Emperor Quang Trung . Nguyễn Huệ was now in control of a united Vietnam , more than twice as large than before . He took the title of Emperor under the reign name Quang Trung . Under his reign the imperial capital Thăng Long was briefly renamed Bắc Thành ( " North City " ) before after his reign taking the modern name Hà Nội ( Hanoi ) . He distributed land to poor peasants , encouraged hitherto suppressed artisans , allowed religious freedom , re - opened Vietnam to international trade , and replaced Classical Chinese with a Vietnamese vernacular written with Chinese characters , as the official language . The ambitious character of Quang Trung is legendary in Vietnamese history . He ordered the melting of Vietnamese coins to make cannons , and seized the Chinese provinces of Guangxi and Guangdong . Several stories tell of his ambitious plans and indirect challenge to Qianlong . Quang Trung even proposed to marry one of Qianlong ' s daughters , an indication of his intention to claim Chinese territory . In early 1792 , Quang Trung planned the final assault on the remaining base of Nguyễn Ánh ' s around Saigon , both by sea and land . While waiting for the seasonal winds to change direction into a tailwind to propel his navy , he suddenly collapsed and died of unknown causes at the age of 40 . Many Vietnamese believe that if he had ruled for another ten years , the fate of the country would have been significantly different . Decline and fall . After Emperor Quang Trung ' s death , his son Nguyễn Quang Toản was enthroned as Emperor Cảnh Thịnh at the age of ten . However , the real power was in the hands of his uncle Bui Dac Tuyen , who enacted a massive political purge . Many who served under Quang Trung were executed , while others became discouraged and left the regime , considerably weakening the Tây Sơn . This paved the way for Nguyễn Ánh to capture the entire country within 10 years , with the help of French military adventurers enlisted by French bishop Pigneau de Behaine . In 1800 , Nguyễn Ánh occupied Quy Nhon citadel . In 1801 , he occupied Phú Xuân , forcing Nguyễn Quang Toản to flee to Thăng Long . In 1802 , Anh besieged Thăng Long . The then 20 - year old Nguyễn Quang Toản escaped , but then was captured and executed , ending the dynasty after 24 years , and the Nguyễn , the last imperial dynasty of Vietnam , took over the country in 1802 .