Yamaguchi Prefecture (山口県, Yamaguchi-ken^?) is a prefecture of Japan in the Chūgoku region of the main island of Honshu. The capital is the city of Yamaguchi, in the center of the prefecture. The largest city, however, is Shimonoseki.

Yamaguchi Prefecture was created by the merger of the provinces of Suō and Nagato. During the rise of the samurai class during the Heian and Kamakura Periods (794–1333), the Ouchi family of Suō Province and the Koto family of Nagato Province gained influence as powerful warrior clans. In the Muromachi Period (1336—1573), Ouchi Hiroyo, the 24th ruler of the Ouchi family conquered both areas of Yamaguchi Prefecture. The Ouchi clan imitated the city planning of Kyoto. They gained great wealth through cultural imports from the continent and trade with Korea and Ming Dynasty China. As a result, Yamaguchi came to be known as the "Kyoto of the West," and Ouchi culture flourished. Sue Harutaka defeated the 31st ruler of the Ouchi clan. The Sue clan was then defeated by Mōri Motonari, and the Mōri family gained control of the Chugoku region. Yamaguchi was ruled as part of the Mōri clan domain during the Sengoku period. Mōri Terumoto was then defeated by Tokugawa Ieyasu in the battle of Sekigahara in 1600. He was forced to give up all his land except for the Suō and Nagato areas (current-day Yamaguchi Prefecture), where he built his castle in Hagi. Mōri sought to strengthen the economic base of the region and increase local production with his Three Whites campaign (salt, rice, and paper).

...
Wikipedia