Yamaguchi Prefecture has been influenced by the nearby Asian Continent since as early as the 2nd and 3rd centuries BC, when wetland rice cultivation methods began. Between the 4th and 5th centuries AD, the Yamato Imperial Court unified Japan under a national government. Yamaguchi Prefecture was made up of seven counties which were integrated into the two provinces of Suo and Nagato in the 7th century.
During the rise of the samurai class during the Heian and Kamakura Periods (794 - 1333), the Ouchi family of Suo Province and the Koto family of Nagato Province gained influence as powerful warrior clans. In the Muromachi Period (1338 - 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 and accumulated great financial power through cultural imports from the continent and trade with Korea and the Ming Dynasty in China. As a result, Yamaguchi came to be known as the "Kyoto of the West," and the impressive Ouchi Culture flourished.
However, the 31st ruler of the proud Ouchi clan was defeated by Sue Harutaka. The Sue clan was then defeated by Mori Motonari, and the Mori family gained control of the Chugoku region.
Mori was then defeated by Tokugawa Ieyasu in the battle of Sekigahara in 1600 and was forced to give up all his land except for the Suo and Nagato areas, where he built his castle in Hagi City. Mori then began his attempt to strengthen the economic base of the region and increase local production with his 'Three Whites' campaign (salt, rice, and paper). At the end of the Edo Period, a lot of energy was invested in education, producing successive men of talent such as Yoshida Shoin and Takasugi Shinsaku. They were a driving force in the Meiji Restoration and played a significant role in the formation of the modern Japanese nation.
Four years after the Edo Shogunate was overthrown and the Meiji government formed in 1868, the present Yamaguchi Prefecture was established. The Meiji government brought in many new systems and modern policies, and promoted the introduction of modern industry. Cement production and silk thread production factories were set up in Yamaguchi Prefecture, and although this was the beginning of modern industry, Meiji Period Yamaguchi was generally centered around agriculture. In the Taisho period, shipbuilding, chemical, machinery, and metal working plants were built one after another in Yamaguchi's harbors in the Seto Inland Sea area, which are blessed with abundant minerals and natural resources. In the Showa Period, when the Petroleum collective was formed after the war, Yamaguchi continued to develop, and became one of the most industrialized prefectures in the country.