Kai Province (甲斐国,Kai-no-kuni) was aprovince of Japan in the area of Japan that is todayYamanashi Prefecture.[1] Kai bordered onSagami,Suruga,Shinano andMusashi Provinces. Its abbreviated form name wasKōshū (甲州). The origin of its name is uncertain. It lies in centralHonshū, west ofTokyo, in a landlocked mountainous region that includesMount Fuji along its border with modernShizuoka Prefecture.
Kai was one of the original provinces of Japan established in theNara period under theTaihō Code. The original capital of the province was located in what is nowFuefuki. Under theEngishiki classification system, Kai was ranked as a "superior country" (上国) in terms of importance, and one of the 16 "middle countries" (中国) in terms of distance from the capital. Although not directly on theTōkaidō, it was also included as one of the Tōkaidō provinces.
Numerous remains from theKofun period have been found in Kai. During theHeian period, the area came under the control of theKai Genji, who controlled the province throughout theKamakura period. During theSengoku period, a branch of the clan, theTakeda clan rose to prominence. The warlordTakeda Shingen, ruled Kai from his stronghold atKōfu and expanded the holdings of the clan to includeShinano andSuruga Provinces, and engaged in constant warfare against theUesugi clan inEchigo Province. After the Takeda were defeated by a coalition led byOda Nobunaga andTokugawa Ieyasu, Kai Province came briefly under the rule of Nobunaga’s retainerKawajiri Hidetaka. After Nobunaga’s assassination at theHonnō-ji Incident, the province was contested between Tokugawa Ieyasu and theGo-Hōjō clan based inOdawara. TheTokugawa clan, theUesugi clan and theHōjō clan each aspired to seize the vast area inShinano Province,Ueno region, and Kai Province, which ruled by the remnants of the many small clans formerly serving Takeda clan, following of disorder post death of Nobunaga, at the same time with Ieyasu departure an army of 8,000 soldiers to those disputed region. This caused the triangle conflict between those three factions in the event which dubbed by historians asTenshō-Jingo War broke out.[2][a] As the war turned in favor of Tokugawa clan, combined with the defection ofSanada Masayuki to the Tokugawa faction, the Hōjō clan now negotiate truce with Ieyasu.[5] The Hōjō clan then sent Hōjō Ujinobu as representative, while the Tokugawa sent Ii Naomasa as representative for the pre eliminary meetings.[6][7] Furthermore, in October, representatives from the Oda clan such asOda Nobukatsu,Oda Nobutaka, and Toyotomi mediated the negotiation until the truce officially concluded.[8]
However, after thedestruction of the Go-Hōjō byToyotomi Hideyoshi in 1590, the province was ruled by a succession of Toyotomi loyalists.
With the establishment of theTokugawa shogunate, Kai was regarded as strategically important to the defense ofEdo due to its position between the Tōkaidō andNakasendō highways, which were connected through Kai Province by theKōshū Kaidō. Kai Province was entrusted briefly to Tokugawa clan members or the highly trustedYanagisawa clan from 1705-1724 asKōfu Domain, but for the most part was retained astenryō territory ruled directly by the shogunate through a succession ofhatamoto-classdaikan.
After theMeiji Restoration, Kai province was renamedKōfu Prefecture in 1869. With theabolition of the han system in 1871, it was renamedYamanashi Prefecture.
Kai Province consisted of nine districts (originally consisted of traditionally four):
Media related toKai Province at Wikimedia Commons