Iwate

Iwate was a district of northern Mutsu, in the upper Kitakami country of northeastern Honshu. Its later medieval history became closely tied to the rise of the Nanbu, whose power expanded southward from Nukanobu. In 1588 Nanbu Nobunao defeated the Shiba house; in 1590 Toyotomi Hideyoshi confirmed his possession of seven northern districts. The following year Nobunao decided to move his principal seat from Sannohe to Kozukata.

The new castle occupied a hill where the old Kitakami and Nakatsu rivers met, on the site of an earlier stronghold held by the Fukushi. Construction traditionally began in 1597 and proceeded fully after formal permission in 1598. Stone walls enclosed the main and outer compounds, while moats extended into the developing settlement. Bridges built across the Nakatsu between 1609 and 1612 helped join its quarters. Morioka emerged as the domain centre through the Edo period. Within the wider Iwate district, the castle and its town gave Nanbu authority a durable administrative focus, tying river crossings and settlement growth to the consolidation of warrior government.