The Trịnh–Nguyễn Civil War (Vietnamese: Trịnh-Nguyễn phân tranh; Hán tự: 鄭阮紛爭) was a 17th-century lengthy civil war waged between the two ruling families in Vietnam, the Trịnh lords of Đàng Ngoài and the Nguyễn lords of Đàng Trong, centered in today's Central Vietnam. The wars resulted in a long stalemate and century of peace before conflicts resumed in 1774 resulting in the emergence of the Tây Sơn forces following Trịnh Lords at the time. During the division of Vietnam, Gianh River was used as the border between two regimes Đàng Ngoài and Đàng Trong.