[1] In the late Nara period, after the establishment of a centralized government under the Ritsuryō system, the imperial court sent a number of military expeditions to what is now the Tōhoku region of northern Japan to bring the local Emishi tribes under its control.

[2] The Emishi were able to successfully resist the Japanese for several decades; however, in 802 AD, the Chinjufu-shōgun Sakanoue no Tamuramaro led an expedition with 4000 troops from the ten provinces of eastern Japan (Suruga, Kai, Sagami, Musashi, Kazusa, Shimōsa, Hitachi, Shinano, Kōzuke and Shimotsuke) and built Isawa Castle as his stronghold within Emishi territory in the valley of the Kitakami River.

In 803 AD, Shiwa Castle was established in what is now part of the city of Morioka to serve as an administrative center of the imperial government.

The garrison at Isawa Castle was reduced to 700 men in 815 AD, of whom many were local Emishi (known as Fushū (俘囚)) in the service of the imperial court.

By the middle of the 9th century, mention of Isawa Castle largely disappears from the historical record, although it reappears as a stronghold of Abe no Munetō in the Zenkunen War against the forces central government led by Minamoto no Yoriyoshi.