Battle of Shōbunuma
Date: Spring of Bunmei 12 (1480)
Location: Shōbunuma in the Sagae manor of Dewa Province
Synopsis: In the midst of historical tensions between the Date and Sagae clans of Dewa, Date Shigemune, the twelfth head of the Date clan, ordered Koori Muneyoshi to attack the Sagae. The first attempt, in the winter of 1479, failed owing to the lack of mobility caused by snowfall. During a second attempt in the spring of 1480, an ambush by the Sagae (with support from members of the Mizonobe and Aterazawa clans) scattered the Date forces during which Muneyoshi took his own life.
The Battle of Shōbunuma occurred in the spring of Bunmei 12 (1480) in Shōbunuma in the Sagae manor in Dewa Province. The conflict was waged between the Date and Sagae clans.
The Sagae clan descended from Ōe no Hiromoto, the first head of the mandokoro, or central political organ, of the Kamakura bakufu. From the Kamakura period, the clan established itself at the Sagae manor. During the Nanbokuchō period (1337 to 1392), the Sagae fought on behalf of the Southern Court, but lost against Shiba Kaneyori at the Battle of Urushigawa in 1368. Thereafter, the Sagae submitted to the Mogami clan (descendants of the Shiba clan) who served as the unshū-kanrei, or deputy shōgun of Dewa. Meanwhile, in the era of Date Masamune (Daizen-notaifu), the ninth head of the clan from the late Nanbokuchō to early Muromachi periods, he received his formal wife, Rantei Myōgyoku-zenni, from the Ashikaga shōgun family, and, in 1385, expanded into the Okitama District of Dewa. As a consequence, the Date and Sagae clans held territories on each side of the Gohyakugawa Gorge separated by the Mogami River.
In the Muromachi period, the Date clan became members of the Kyōto-fuchishū, a group of clans from the Kantō and Tōhoku regions who maintained a direct subservient relationship with the shōgun of the Muromachi bakufu. In contrast, the Sagae clan stood alongside the Kamakura administration and, in 1401, dispatched soldiers to assault Kanda Castle held by the Date.
To compel the Kokubun clan of Mutsu to submit to them, the Date clashed with them on three occasions between 1467 and 1472, but the Sagae clan supported the defense of the Kokubun.
Course of events
In the winter of 1479, Date Shigemune, the twelfth head of the Date clan, ordered Koori Muneyoshi to attack Sagae Castle. At this time, Sagae Tamehiro served as the twelfth head of the Sagae clan. The Sagae and Aterazawa clans were engaged in a separate dispute so the Mizonobe clan mediated a settlement evidenced by written pledges sealed in blood in the hall of the Maitreya (Bodhisattva) at the Jion Temple in Sagae. Owing to the accumulation of snowfall, Muneyoshi could not maneuver his troops as desired and, without fighting, withdrew his forces.
In the spring of 1480, after Muneyoshi launched another attack, the Sagae clan enticed them to Shōbunuma whereupon soldiers from the Mizonobe and Aterazawa clans ambushed them, causing the collapse of the Date forces. After sustaining several injuries, Muneyoshi gave-up attempts to flee and took his own life by stabbing his chest with a long sword.
Koori Munetoshi, Muneyoshi’s son and designated heir, appealed to Mogami Mitsuuji to construct the Kooriyama-Matsuzō sub-temple in a mountainous area near the Jion Temple to worship Muneyoshi and serve as the family temple. The Sagae clan, under the command of the Mogami clan, acquired a degree of autonomy but also strengthened their familial ties to the Mogami through marriage. In 1483, three years after this battle, members of the Date clan traveled to Kyōto to provide splendid gifts to Ashikaga Yoshihisa, the ninth shōgun of the Muromachi bakufu, thereby raising their own authority.