Trịnh Tráng
In 1620, Nguyễn Phúc Nguyên officially refused to send taxes to the court in Hanoi. A formal demand was made to the Nguyễn to submit to the authority of the court, and it was formally refused. In 1623 Trịnh Tùng died and was succeeded by his son Trịnh Tráng. Now Trịnh Tráng made a formal demand for submission, and again Nguyễn Phúc Nguyên refused. Finally in 1627 open warfare broke out between the Trịnh and the Nguyễn. For four months a large Trịnh army battled against the Nguyễn army but were unable to defeat them. The result of this war was that Vietnam had effectively been partitioned into northern and southern regions, with the Trịnh controlling most of the north and the Nguyễn controlling most of the south; the dividing line was the Gianh River in Quảng Bình Province. This border was very close to the Seventeenth parallel (in actuality the Bến Hải River located just to the south in Quảng Trị Province), which was imposed as the border between North Vietnam and South Vietnam during the Partition of Vietnam (1954–75).