Nagato Province was in the Sanyōdō, or Sanyō Region, an area encompassing provinces in the western portion of Honshū along the Seto Inland Sea. Nagato is situated at the westernmost end of Honshū with most of its coastline along the Sea of Japan and a smaller portion along the Seto Inland Sea. Owing to its location across from the Korean peninsula, Nagato had an important role in foreign trade, diplomacy, and defense. In 1523, a confrontation occurred between the Ōuchi and the Hosokawa known as the Ningbo Incident over trading rights with China, after which the Ōuchi secured exclusive rights to trade with the Ming rulers in China.
In current terms, Nagato Province corresponds to the western half of Yamaguchi Prefecture. The province was comprised of six districts including Asa, Toyoura, Mine, Ōtsu, Abu, and Mishima. The city of Shimonoseki served as the provincial seat of government and is the westernmost city on Honshū.
During the Sengoku period, Nagato and neighboring Suō Province were governed by the Ōuchi clan. The Ōuchi were based in the city of Yamaguchi in Suō. The Washizu and Naitō clans of Nagato served the Ōuchi.
1465-1495: Ōuchi Masahiro
1495-1528: Ōuchi Yoshioki
1528-1551: Ōuchi Yoshitaka
1562-1563: Mōri Takamoto
- Ōuchi clan
- Sue clan
- Mōri clan
1557: After being surrounded by the Mōri army, Ōuchi Yoshinaga killed himself in the Chōfuku Temple in the Chofu District of Shimonoseki, marking the end of the Ōuchi clan.
Sumiyoshi: Originally built in the tenth century, the main hall was constructed in 1370 and designated a national treasure. The shrine was neglected during the Sengoku period until restored upon orders of the Ōuchi and Mōri.