The area of present-day Ōshū was part of ancient
Mutsu Province, and has been settled since at least the
Japanese Paleolithic period.
Isawa is especially rich in
Kofun Period remains from the 5th century. By the
Nara period, Japanese hunters, trappers, settlers and itinerant missionaries were visiting and settling in this area, and coming into contact with the native
Emishi people. In 729,
Kokuseki-ji temple claims to have been established by the Buddhist priest
Gyōki in a mountainous area to the east of the Kitakami River in what is now
Mizusawa. In 776, two separate attacks were launched by the
imperial dynasty against the Emishi with little success. In June 787 Emishi cavalry led by
Aterui and More surprised and routed a larger force of Japanese infantry in the Battle of Subuse (located in what is now part of Mizusawa). Despite these successes the Emishi could not hold out against the Japanese and in 802 Aterui and More surrendered and were beheaded. That same year
Sakanoue no Tamuramaro, established
Isawa Castle. Despite the victory the Japanese found if difficult to rule the territory directly. Six semi-autonomous districts were established along the
Kitakami River. Eventually these came under the control of a powerful Emishi clan from Appi, the
Abe clan. Early in the 11th century
Abe no Yoritoki refused to pay taxes to the central government, led raiding parties south of the Koromo River, and generally ruled as an independent monarch. This led to the or Early Nine-Years War (1050 - 1062), in which
Minamoto no Yoriyoshi reinforced by Kiyohara no Takenori from
Dewa Province defeated the Abe clan. The area later came under the rule of the
Kiyohara clan. Corrupt administration by the Kiyohara led to the
Gosannen War (後三年合戦) or Latter Three Years' War (1083 - 1087) in which
Minamoto no Yoshiie subdued the Kiyohara.
Fujiwara no Kiyohira, the founder of the
Ōshū Fujiwara dynasty, was born in Fort Toyota which is now in the Iwayado area of
Esashi. Around 1100, he relocated to
Hiraizumi where he and his descendants ruled for nearly a hundred years. In 1348, a Zen Buddhist priest named Mutei Ryōshō founded the temple of Shōbō-ji near Kokuseki-ji temple in Mizusawa. It is the third head temple of the
Sōtō sect of Zen Buddhism and boasts the largest thatched roof in Japan. During the
Sengoku period, the area came under control of the powerful
Date clan. During this period, Italian
Jesuit missionaries regarded it as a kingdom. which they called "Voxu". Following the
Battle of Sekigahara, the
Tokugawa shogunate confirmed the area was part of
Sendai Domain under
Date Masamune. One of his retainers was a certain Juan Gotō who commanded Date Masamune's gun regiment at Osaka in 1614 and 1615. He was also a
Kirishitan and established a church in the Fukuwara area of Mizusawa. After Christianity was outlawed in 1623 he went into hiding to escape capture. Foreign missionaries continued to visit the area in secret until December 1623 when the Jesuit Padre Diogo de Carvalho from Portugal was captured on the upper reaches of the Isawa River, sent to Sendai and forced to stand in the frozen Hirose River until he died in the early hours of what was then New Year's Day, namely February 19, 1624. There is a memorial to Juan Gotō in the Fukuwara area and many crypto-Christian remains can still be seen in that neighborhood. Following the
Meiji restoration, the area was assigned to
Iwate Prefecture rather than
Miyagi Prefecture as part of the governments efforts to break up former
Sendai Domain, partly due to its role in opposing the
Meiji government during the
Boshin War. The town of
Mizusawa was created within
Isawa District on April 1, 1889, with the establishment of the modern municipalities system. It was raised to city status on April 1, 1954. The village of
Esashi was likewise created on April 1, 1889, raised to town status on February 10, 1955, and to city status on November 3, 1958. The city of Ōshū was established on February 20, 2006, from the merger of the cities Esashi and Mizusawa with the towns of
Isawa and
Maesawa, and the village of
Koromogawa. ==Government==