Battle of Sezawa
Date: Third month of Tenbun 11 (1542)
Location: Sezawa near the border of Shinano and Kai provinces
Outcome: Despite incurring more losses, the Takeda stopped an invasion at the border by the combined forces of the Suwa and Ogasawara.
The Battle of Sezawa occurred in the third month of Tenbun 11 (1542) in Sezawa in Shinano Province. The conflict was waged between Takeda Harunobu, the military governor of Kai Province and the combined armies of Suwa Yorishige (a sengoku daimyō, the nineteenth head of the Suwa clan and lord of Uehara Castle) and Ogasawara Nagatoki, the military governor of Shinano.
On 6/14 of 1541, Takeda Nobutora, the head of the Kai-Takeda clan, faced a coup d’état by family members and hereditary retainers of the clan who backed his eldest son, Takeda Harunobu, leading to his ouster to the territory of Imagawa Yoshimoto, the military governor of Suruga Province with whom Nobutora had a marital alliance. After Nobutora unified Kai, he began attacking the neighboring province of Shinano, but, in parallel, he had his daughter, Nene (Harunobu’s younger sister), wed Suwa Yorishige, the head of the main branch of the Suwa family. However, owing to the removal of Nobutora, the marital alliance between the Takeda and Suwa families became fragile.
In the third month of 1542, Yorishige noted that Harunobu’s political administration was not yet solidified, so he made plans with Ogasawara Nagatoki to invade Kai. Harunobu responded by leading a deployment to confront the Suwa and Ogasawara forces at the border between Shinano and Kai provinces. As violent clashes unfolded, the Takeda army (which had not yet coalesced under their new leader) incurred more losses than the combined forces of the Suwa and Ogasawara. However, Harunobu set-up a main base in Sezawa and fought back decisively, finally causing the invading forces to retreat.
Nevertheless, information concerning this battle does not appear in authoritative sources. The Takeda clan maintained an alliance until the invasion of the Chiisagata and Saku districts by the Takeda, Murakami, and Suwa armies in 1541. On 6/14, after returning to Kai, Nobutora was expelled by Harunobu. On 7/14, after Uesugi Norimasa, the deputy shōgun of the Kantō deployed to the Saku District in Shinano, Yorishige reconciled with Norimasa without informing the Takeda and Murakami clans and divided the territory. On 7/2 of 1542, Harunobu commenced an invasion of the Suwa District and vanquished the main branch of the Suwa family in an event known as the Battle of Kuwabara Castle. This is considered to have taken place in the context of Yorishige breaching the alliance with the Takeda and Murakami by entering into an agreement with Uesugi Norimasa without their participation.
Under one theory, the Battle of Sezawa was fabricated years later to justify the elimination of the Suwa clan by the Takeda and questions remain whether the battle actually occurred.