Trịnh Tạc (Hán: 鄭柞; 11 April 1606 – 24 September 1682) ruled northern Dai Viet in 1657–1682. Trịnh Tạc was one of the most successful of the Trịnh lords to rule northern Vietnam. During his rule, he made peace with the Nguyễn, beginning a century of peace in Vietnam. Trịnh Tạc also ended the last remnants of the pretender Mạc dynasty. Early career In 1648 Trịnh Tạc gained more political power in the court as his father Trinh Trang’s health failed. In 1649 the Dutch reported that the young king Le Duy Huu and his uncle had allegedly poisoned Trịnh Tạc. In 1655, Nguyễn forces advanced to Nghe An, threatening the Trịnh regime. The situation became so critical that in the autumn of that year, Trịnh Tạc and reinforcements arrived at the battlefield, managed and drove the Nguyễn back to the Gianh River. In the next year, the southerners launched a naval attack on Nghe An and Trịnh Tạc sent his eldest son Trịnh Căn with a new army to confront the Nguyễn. While Trịnh Tạc's brother Trinh Toan was the commander-in-chief of the northern army, Trịnh Tạc himself distrusted his brother. Nonetheless, Trịnh Tạc finally stopped the southern advanced in mid-1656. The Nguyễn continued occupying Nghe An and Ha Tinh, and a large number of northern Vietnamese who defected to the Nguyễn were allowed to resettle further south. Lord of Tonkin Military campaigns In 1658 the Nguyễn resumed their offensive, reaching the northern border of Nghe An near Quynh Luu. By the end of the year Trịnh Căn had pushed the southerners back to southern banks of the Ca River. Fighting between the Trịnh and the Nguyễn came to a lull in the next two years, 1659 and 1660. Trịnh Tạc's agents rushed into villages in enemy's occupying territories, lowering the Nguyễn morale. In late 1660 Trịnh Tạc planned for an extensive military preparation against the Nguyễn regime in the south and to fend off a potential Qing offensive, which ultimately had little success. In 1667 Trịnh Tạc's army moved north and attacked the Mạc remnants in Cao Bang, who were formerly under Ming protection. However the new Qing empire continued to support the Mạc and forced the Trịnh to withdraw. In 1671 he sent a request to the Dutch government in Batavia to assist his last military campaign against the Nguyễn in the south. The Dutch did nothing