Thuận Hóa(順化) was a historic territory in central Vietnam. It consisted of the modern provinces of Quảng Bình, Quảng Trị, and Thừa Thiên–Huế (historically, Thừa Thiên–Thuận Hóa).
In 1306, the king of Champa, Che Man, offered Vietnam two Chăm prefectures, Ô and Lý, in exchange for a marriage with the Vietnamese princess Huyền Trân. The Vietnamese king Trần Anh Tông accepted this offer, then took and renamed Ô prefecture and Lý prefecture as Thuận prefecture and Hóa prefecture. These prefectures soon began to be referred to collectively as the Thuận Hóa region. From this time, Thuận Hóa was a territory where the Vietnamese, Chăms, and Lao frequently fought one another. In 1466, during the reign of king Lê Thánh Tông, Thuận Hóa became one of the 12 prefectures of Vietnam and later became a province of Vietnam.
In 1592, the Mạc Dynasty lost their war against Lê loyalists and was forced to flee to Cao Bằng, whereupon the Lê kings was restored as de jure Vietnamese rulers. Shortly afterward, Nguyễn Kim, the leader of the Lê Dynasty loyalists and the de facto ruler of Vietnam, was poisoned by a Mạc Dynasty general. Kim's son-in-law, Trịnh Kiểm, took over the leadership and assassinated Kim's eldest son, Nguyễn Uông, in order to secure his authority. Nguyễn Hoàng, another son of Nguyễn Kim, feared having a fate like his brother Nguyễn Uông so he pretended to have mental illness and asked his sister Ngoc Bao, who was a wife of Trịnh Kiểm, to entreat Kiểm to allow Hoàng to govern Thuận Hóa, the southernmost region of Vietnam at this time. Because Mạc Dynasty loyalists were revolting in Thuận Hóa and Trịnh Kiểm was busy fighting the remaining Mạc Dynasty forces in northern Vietnam during this time, Ngoc Bao's request was approved and Nguyễn Hoàng went south. After Hoàng pacified Thuận Hóa, he and his successor Nguyễn Phúc Nguyên secretly made this region loyal to the Nguyễn family; then they rose against the Trịnh Lords. Vietnam erupted into a new civil war between two de facto ruling families: the clan of the Nguyễn Lords and the clan of the Trịnh Lords. The Nguyễn lords continuously developed the territory and turned it into a strong base for their war against the Trịnh Lord and their expansion to the south. During this time, Thuận Hóa territory spanned from Quảng Bình to Thua Thien-Hue. After the foundation of Nguyễn Dynasty, emperor Gia Long made Thuận Hóa territory a part of Vùng Kinh kỳ (Capital territory), one of three administrative divisions of Vietnam at this time. In mid-1945; the name of Thuận Hóa was restored by Vietnamese prime minister Trần Trọng Kim but it quickly got abandoned after the decline of the Empire of Vietnam.
Other names 
In the West, Thuận Hóa was also known as Sinoa, Singoa, or Senna.
- Chapius, p. 85.
- Phan Khoang, p. 85.
- Chapius, p. 119.
- Phan Khoang, pp. 108-110.
- Trần Trọng Kim, pp. 275-276.
- Trần Trọng Kim, pp. 281-283.
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