The Battle of Jugorigahara (十五里ヶ原の戦い)
During the Battle of Jugorigahara, which was fought in September and October 1588, the allied troops of Kagekatsu UESUGI and Yoshikatsu DAIHOJI, led by Shigenaga HONJO, fought against Yoshiaki MOGAMI's troops, which were led by the brothers Yoshinaga and Katsumasa TOZENJI.
The Daihoji Muto clan had ruled the Shonai district of Dewa Province for generations. They were suffered from the successive disturbances within the family during the Warring States period. The Shonai district received high economic benefits based on its inclusion of the Shonai plains and Sakata Minato port, so various clans including Uesugi, Mogami and Onodera watched for an opportunity to plunder this area.
During the 1580s, when the lord of Yamagatajo Castle, Yoshiaki MOGAMI, who was rapidly expanding his territory, launched an attack on the Shonai district, the lord of Ourajo Castle, Yoshiuji DAIHOJI, confronted Mogami's troops with the help of Shigenaga HONJO, who had been an alliance from the days of his father Yoshimasu DAIHOJI. In 1583, using Yoshinaga TOZENJI, a senior vassal of the Muto clan and the lord of Tozen-ji Castle, Yoshiaki assassinated Yoshiuji. Yoshiaki, while continuing his attack, killed Yoshiuji's younger brother and successor as the head of the family, Yoshioki DAIHOJI, during November and December 1587. When Yoshiaki plundered the Shonai district, he directed the Tozenji clan to rule the district. Subsequently, Shigenaga HONJO's son Yoshikatsu DAIHOJI, who had been adopted by Yoshioki DAIJOJI, was determined to resume his power while taking refuge with his biological father. As a result, the Muto clan was left completely under the influence of the Uesugi clan.
When Masamune DATE intervened in an internal disturbance of the Osaki clan by using force, which is called the Battle of Osaki in January and February 1588, since the Osaki family was the head house of the Mogami family as well as the family home of Yoshiaki's lawful wife, Yoshiaki sent reinforcements to Osaki's territory. At the same time, by sending troops to Date's territory, Yoshiaki captured a portion of his territory. Kagekatsu UESUGI sent troops to conquer the Shonai district, by taking advantage of the situation in which Yoshiaki was busily occupied with the battle against Masamune.
Development of the battle
Kagekatsu UESUGI directed Shigenaga HONJO and Yoshikatsu MUTO to attack Oura-jo Castle in September and October. On the other hand, the Tozenji brothers decided to meet the enemy in the field; so the troops confronted one another at Jugorigahara.
Although the battle was initially a pitched battle, the Uesugi's allied troops, who outnumbered those of Mogami, gradually drove their opponent into a corner. Yoshinaga TOZENJI charged the opponent's headquarters and died there. When Katsumasa was informed of his brother's death, he also charged the opponent's headquarters alone and made a surprise attack on Shigenaga HONJO with his sword; but he was killed by Shigenaga and his close retainers.
Katsumasa's stroke was so heavy that a part of Shigenaga's helmet was cut off from the region of the temple to below the ear
The sword Katsumasa used at this time was the noted Masamune sword, which was later passed into the hands of Shigenaga HONJO to be renamed Honjo Masamune (the noted sword "Masamune" once owned by Shigenaga HONJO).
The Mogami's troops were defeated despite their continual resistance at places including Asahiyama-jo Castle; consequently, the Shonai district was incorporated into the territory of Kagekatsu UESUGI. Shigenaga advanced his troops further as he was spurred by his side's victory, but he was obliged to withdraw due to a fierce counter-offensive by the Mogami troops at Higashine.
After the battle
The battle broke out after the proclamation of a cease-fire edict for the Ou region issued by Hideyoshi TOYOTOMI in December 1587 and January 1588; which means that the allied dispatch of the troops by Uesugi should have been unlawful. But Yoshikatsu MUTO's reinstatement as a ruler of the Shonai district was overlooked by Hideyoshi. When Yoshikatsu was punished by being deprived of his fief the Shonai district in 1591, the district was given to Kagekatsu UESUGI. Yoshiaki MOGAMI had a deep hatred for Hideyoshi and the Uesugi clan, becauase he was infuriated by the decisions made by Hideyoshi and because he was grievously shocked by the death of his daughter Komahime, who was a concubine of Hidetsugu TOYOTOMI and, as instructed by Hideyoshi, executed in the Hidetsugu Incident. Therefore, Yoshiaki MOGAMI sided with Ieyasu TOKUGAWA in the Battle of Sekigahara.
Yoshiaki MOGAMI won back the Shonai district from Uesugi in May and June 1601.