The degenerated Le dynasty, which had endured under ten rulers between 1497 and 1527, in the end was no longer able to maintain control over the northern part of the country, much less the new territories to the south.

The weakening of the monarchy had created a vacuum that the various noble families of the aristocracy are eager to fill.

In 1527 Mac Dang Dung, a scholar-official who has effectively controlled the Le for a decade, had seized the throne, prompting other families of the aristocracy, notably the Nguyen and Trinh, to rush to the support of the Le.

An attack on the Mac forces led by the Le general Nguyen Kim results in the partition of Vietnam in 1545, with the Nguyen family seizing control of the southern part of the country as far north as what is now Thanh Hoa Province.

The Nguyen, who take the hereditary title chua, continue to profess loyalty to the Le dynasty.

By the late sixteenth century the Trinh family has ousted the Mac family and has begun to rule the northern half of the country also in the name of the Le dynasty.

The Trinh, who, like the Nyuyen, take the title chua, spend most of the seventeenth century attempting to depose the Nguyen

In order to repulse invading Trinh forces, the Nguyen in 1631 complete the building of two great walls, six meters high and eighteen kilometers long, on their northern frontier.

The Trinh, with one hundred thousand troops, five hundred elephants, and five hundred large junks, are numerically far superior to their southern foe.

The Nguyen, however, are better equipped, having by this time acquired Portuguese weapons and gunpowder, and, as the defending force, have the support of the local people.

In addition, the Nguyen have the advantage of controlling vast open lands in the Mekong Delta, wrested from the Khmer, with which to attract immigrants and refugees from the north.

Among those who take up residence in the delta are an estimated three thousand Chinese supporters of the defunct Ming dynasty, who arrive in 1679 aboard fifty junks and set about becoming farmers and traders.

The Nguyen, aided by the Chinese settlers, will succeed in forcing the Khmer completely out of the Mekong Delta by 1749.