The prefecture is landlocked, featuring a fertile central valley, the Kōfu Basin, surrounded by many of the highest mountains in Japan including the highest, Mount Fuji located on the southern border with Shizuoka.

The capital of the prefecture is the city of Kōfu.

As in most other Japanese regions, prehistoric society in Yamanashi progressed though the hunting, fishing and gathering stage of the Jōmon period, then the rice-producing stage of the Yayoi period and subsequent village and regional formation. The Maruyama and Choshizuka Kofun (earthen burial mounds) located on Sone Hill of Nakamichi Town (Southern Kōfu) are believed to have been built from the end of the 4th century. From these remains it can be assumed that the people of Sone Hill had great influence.

During the Heian period, Kai Province was created in this area.

Among the many Kaigenji generations, those of the Takeda, Ogasawara, and Nanbu families were particularly prosperous. During the Sengoku period of the 16th century, Takeda Shingen attained the status of daimyō and built Tsuzuji Mansion and the Yōgai Castle in Kōfu. From this base, he attempted to unify and control Japan.

After Takeda’s death in 1582, Kai-no-Kuni came under the control of the Oda and Toyotomi clans before being subsumed into the Tokugawa shogunate during the Edo period. Beneath the Edo shogunate, the Kofu clan (based in Kuninaka, or Central and Western Yamanashi) and the Yamura clan (based in Gunnai, or Eastern Yamanashi) were formed, but in 1724 the area came under the direct control of the Shogunate. With the development of the Kōshū Kaidō (highway) and Fuji River transport, goods, materials and culture flowed into the region.

...
Wikipedia