Battle of Saruyama
Date: Eighth month of Daiei 3 (1523)
Location: Mount Saru in Utsunomiya in Shimotsuke Province
Synopsis: Once former allies, the Utsunomiya and Yūki clans had a falling out after Utsunomiya Tadatsuna succeeded Utsunomiya Shigetsuna as the head of the Shimotsuke-Utsunomiya family. While the Utsunomiya were beset with internal conflict, Yūki Masatomo sought to exploit the situation by joining forces with Haga Takatsune to invade the Utsunomiya territory. After losing the battle, Tadatsuna attempted to return to his home base but was blocked by retainers who rebelled against him and backed Utsunomiya Okitsuna as his successor.
The Battle of Saruyama occurred in the eighth month of Daiei 3 (1523). The conflict was waged between Yūki Masatomo and Utsunomiya Tadatsuna in Shimotsuke Province.
Course of events
The Utsunomiya and Yūki clans formed an alliance when Utsunomiya Shigetsuna had his eldest sister wed Yūki Masatomo. During the Eishō Conflict that occurred in the early part of the sixteenth century, the two clans plotted to back Ashikaga Takamoto as the Koga kubō (the Kantō branch of the ruling Ashikaga family) and, in the course of maintaining a strong relationship, fought together at the Battle of Takebayashi. In the wake of his death, Shigetsuna was succeeded by his son, Utsunomiya Tadatsuna, causing material changes to the relationship between the Utsunomiya and Yūki clans. After the Battle of Yūki in 1440, the twelve townships of Nakamura located in the border area between the respective territories of the two clans fell under the control of the Utsunomiya, whereupon the Utsunomiya assigned a renowned bushō named Nakamura Genkaku to be stationed at Nakamura Castle on the front lines. The contest between the clans for control over these townships intensified. Owing to the efforts of Shigetsuna, around this time the Utsunomiya garnered the authority of the Koga kubō, becoming the most powerful clam in northern Kantō. With the aim of further promoting the clan, Tadatsuna reinforced a hardline approach to governance, but this caused resentment among the retainers, leading to conflict with Haga Takatsune and the Kasama clan. Yūki Masatomo took advantage of the political instability besetting the Utsunomiya and plotted with Takatsune and others to foster conflict with the aim of weakening the Utsunomiya clan.
In the eighth month of 1523, Masatomo invaded the Utsunomiya territory and Utsunomiya Tadatsuna intercepted him at Mount Saru. Nakamura Genkaku defended Nakamura Castle and the twelve townships near the border area, but, at the battle on Mount Saru, the Yūki forces prevailed while members of the Utsunomiya family including Imaizumi Moritaka were killed. The Utsunomiya incurred a major defeat en route to the Yūki recovering their former territory.
Utsunomiya Tadatsuna attempted to withdraw to Utsunomiya Castle, but retainers opposed to Tadatsuna such as Haga Takatsune backed Shigetsuna’s youngest (and still immature) son, Utsunomiya Okitsuna, and launched a rebellion, blocking Tadatsuna from returning to the castle. Tadatsuna turned to a senior retainer who was in conflict with the Haga clan named Mibu Tsunafusa to escape to Kanuma Castle. Under the protection of Tsunafusa, Tadatsuna sought a revival, but the plans did not go well and he died. The band of retainers of the Utsunomiya family used Okitsuna as a puppet administration, and, as a result, members of the Haga and Mibu clans grew increasingly impudent, falling significantly behind neighboring powers. Meanwhile, the Yūki clan succeeded in crushing the formerly robust Utsunomiya clan. Several years later, they succeeded in sending a family member to lead the Oyama clan, becoming the preeminent power in the northern Kantō while experiencing the peak of their prosperity.