Trịnh–Nguyễn War
It was the border between ruling families during the partition of Vietnam following the Trịnh–Nguyễn War of the 17th century, serving to effectively divide the country between northern and southern regions. The 17th parallel used as the border between North Vietnam and South Vietnam from 1954 to 1975 was located just to the south, at the Bến Hải River in Quảng Trị Province.