Nguyen Nhac seizes Qui Nhon, which becomes the Tay Son capital, in 1773.

By 1778 the Tay Son have effective control over the southern part of the country, including Gia Dinh (later Saigon).

The ruling Nguyen family are all killed by the Tay Son rebels, with the exception of Nguyen Anh, the sixteen-year-old nephew of the last Nguyen lord, who escapes to the Mekong Delta.

There he is able to gather a body of supporters and retake Gia Dinh.

The city changes hands several times until 1783, when the Tay Son brothers destroy Nguyen Anh's fleet and drive him to take refuge on Phu Quoc Island.

Soon thereafter, he meets with French missionary bishop Pigneau de Behaine and asks him to be his emissary in obtaining French support to defeat the Tay Son.

Pigneau de Behaine takes Nguyen Anh's five-year-old son, Prince Canh, and departsfor Pondichery in French India to plead for support for the restoration of the Nguyen.

Finding none there, he goes to Paris in 1786 to lobby on Nguyen Anh's behalf.

Louis XVI ostensibly agrees to provide four ships, sixteen hundred and fifty men, and supplies in exchange for Nguyen Anh's promise to cede to France the port of Tourane (Da Nang) and the island of Poulo Condore.

However, the local French authorities in India, under secret orders from the king, refuse to supply the promised ships and men.

Determined to see French military intervention in Vietnam, Pigneau de Behaine himself raises funds for two ships and supplies from among the French merchant community in India, hires deserters from the French navy to man them, and sails back to Vietnam in 1789.

The Tay Son have in the meantime overcome the crumbling Trinh dynasty by 1786 and seized all of the north, thus uniting the country for the first time in two hundred years.

The Tay Son make good their promise to restore the Le dynasty, at least for ceremonial purposes.

The three Nguyen brothers install themselves as kings of the north, central, and southern sections of the country, respectively, while continuing to acknowledge the Le emperor in Thang Long.

In 1788, however, the reigning Le emperor flees north to seek Chinese assistance in defeating the Tay Son.

Eager to comply, a Chinese army of the Qing dynasty (1644-1911) invades Vietnam, seizes Thang Long, and invests the Le ruler as "King of Annam."

This same year, the second eldest Tay Son brother, Nguyen Hue, proclaims himself Emperor Quang Trung.

Marching north with one hundred thousand men and one hundred elephants, Quang Trung attacks Thang Long at night and routs the Chinese army of two hundred thousand, which retreats in disarray.

Immediately following his victory, the Tay Son leader seeks to reestablish friendly relations with China, requesting recognition of his rule and sending the usual tributary mission.

Quang Trung dies in 1792, without leaving a successor strong enough to assume leadership of the country, and the usual factionalism ensues.

By this time, Nguyen Anh and his supporters have won back much of the south from Nguyen Lu, the youngest and least capable of the Tay Son brothers.

When Pigneau de Behaine returns to Vietnam in 1789, Nguyen Anh is in control of Gia Dinh.

In the succeeding years, the bishop brings Nguyen Anh a steady flow of ships, arms, and European advisers, who supervise the building of forts, shipyards, cannon foundries and bomb factories, and instruct the Vietnamese in the manufacture and use of modern armaments.

Nguyen's cause is also greatly aided by divisions within the Tay Son leadership, following the death of Quang Trung, and the inability of the new leaders to deal with the problems of famine and natural disasters that wrack the war-torn country.

After a steady assault on the north, Nguyen Anh's forces take Phu Xuan in June 1801 and Thang Long a year later.