The Chūgoku region, also known as the San'in-San'yō region, is the westernmost region of Honshū, the largest island of Japan. It consists of the prefectures of Hiroshima, Okayama, Shimane, Tottori and Yamaguchi. In 2010, it had a population of 7,563,428.
Chūgoku literally means "middle country", but the origin of the name is unclear. Historically, Japan was divided into a number of provinces called koku, which were in turn classified according to both their power and their distances from the administrative center in Kansai. Under the latter classification, most provinces are divided into "near countries", "middle countries", and "far countries". Therefore, one explanation is that Chūgoku was originally used to refer to the collection of "middle countries" to the west of the capital. However, only five (fewer than half) of the provinces normally considered part of Chūgoku region were in fact classified as middle countries, and the term never applied to the many middle countries to the east of Kansai. Therefore, an alternative explanation is that Chūgoku referred to provinces between Kansai and Kyūshū, which was historically important as the link between Japan and mainland Asia.
Historically, Chūgoku referred to the 16 provinces of San'indō and San'yōdō, which led to the region’s alternative name described below. However, because some of the easternmost provinces were later subsumed into prefectures based primarily in Kansai, those areas are, strictly speaking, not part of the Chūgoku region in modern usage.
In Japanese, the characters and the reading Chūgoku began to be used to mean "China" after the founding of the Republic of China. The same characters are used in Chinese to refer to China, but pronounced Zhōngguó, lit. "Middle Kingdom" or "Middle Country" (Wade Giles: Chung1-kuo2). It is similar to the use of the West Country in English for a region of England.
The city of Hiroshima, the "capital" of the Chūgoku region, was rebuilt after being destroyed by an atomic bomb in 1945, and is now an industrial metropolis of more than one million people.