Lifespan: Kakitsu 3 (1443) (or Bunan 3 (1446)) 10/5 of Meiō 3 to (1494)
Rank: bushō, shugo daimyō
Title: Master of the Office of Palace Repairs
Bakufu: Muromachi – Military Governor of Sagami
Lord: Ashikaga Yoshimasa → Ashikaga Yoshihisa → Ashikaga Yoshitane → Ashikaga Yoshizumi
Father: Uesugi Mochitomo
Siblings: Akifusa, Miura Takahira, sister (formal wife of Uesugi Noritada), Sadamasa, Shukuhō Bonju, Tomomasa, sister (formal wife of Kira Shigetaka), sister (formal wife of Ōishi Fusashige)
Wife: [Formal] Daughter of Nagao Kagenobu
Children: Daughter (wife of Ōishi Akishige), Norikatsu (?)
Adopted Children: Tomoyoshi (natural son of Uesugi Tomomasa)
Uesugi Sadamasa served as a bushō and shugo daimyō during the late Muromachi and Sengoku periods. He was the military governor of Sagami Province and served as the head of the Ōgigayatsu-Uesugi family. He is also known under the name of Ōgigayatsu Sadamasa.
The Ōgigayatsu-Uesugi clan were members of the Uesugi family serving as the deputy shōgun of the Kantō. The Ōgigayatsu were a cadet of the Yamauchi-Uesugi family who served as the military governors of Sagami and succeeded to the role of the deputy shōgun of the Kantō. After the fall of Ashikaga Mochiuji (the fourth Kamakura kubō) against the Yamauchi family in the Eikyō Conflict in 1438, the Ōgigayatsu allied with the Yamauchi. The Ōgigayatsu also supported the Yamauchi in opposition to Mochiuji’s son, Ashikaga Shigeuji (the Koga kubō) during the long-running Kyōtoku Conflict from 1455 to 1483.
Serving as the kasai, or head of house affairs, of the Ōgigayatsu-Uesugi family, Ōta Sukekiyo and Ōta Dōkan constructed Kawagoe and Edo castles, driving a significant expansion of the power of the Ōgigayatsu family. The Yamauchi and Ōgigayatsu families were then called the Two Uesugi Families.
Sadamasa was born as the third son of Uesugi Mochitomo. In 1473, his nephew, Uesugi Masazane, who was the head of the Ōgigayatsu family, was killed in battle against the Koga kubō during the Irako War. Masazane died young without an heir, so, based on a decision by the chief retainers of the Ōgigayatsu including Ōta Dōkan, Sadamasa was chosen to succeed Masazane as the head of the family.
Sadamasa joined Uesugi Akisada, the deputy shōgun of the Kantō and head of the Yamauchi-Uesugi family, to deploy for the Irako War against Ashikaga Shigeuji, the Koga kubō. In 1476, however, Nagao Kageharu, a powerful retainer of the Yamauchi family, rebelled and, in 1477, launched a surprise attack against the base in Irako. In an event known as the Revolt of Nagao Kageharu, Sadamasa and Akisada incurred a major defeat and fled to Kōzuke Province. The Uesugi confronted a crises, but, Ōta Dōkan, the head of house affairs of the Ōgigayatsu, came to the rescue by defeating Kageharu’s supporters one after another, beginning with the Toshima clan. Sadamasa also engaged in battle and defended the base of the Ōgigayatsu clan at Kawagoe Castle.
In 1482, after the downfall of Kageharu, Sadamasa settled with Shigeuji, the Koga kubō. Sadamasa, however, was dissatisfied with the settlement that was driven by the Yamauchi family, which led to a falling out between Sadamasa and Akisada. Moreover, owing to his success in subduing the rebellion, Ōta Dōkan, the head of house affairs, gained prominence, stirring jealousy by Sadamasa. On 7/26 of Bunmei 18 (1486), Sadamasa invited Dōkan to the Kasuya residence in Sagami and assassinated him. While dying, Dōkan purportedly told Sadamasa this act would bring about the end of the clan.
With respect to the reasons for the murder, Sadamasa asserted that the clan retainers resented Dōkan’s monopolization of house affairs and that Dōkan had an intention to betray his lord, Uesugi Akisada (the head of the Ōgigayatsu family). Meanwhile, those who supported Dōkan expressed their mistrust of Sadamasa’s harsh measures. In fact, Sadamasa either feared Dōkan’s influence within the family or, as an alternative theory, Sadamasa was unwittingly used by Akisada as a means to undermine the authority of the Ōgigayatsu clan that had grown through Dōkan.
Owing to the murder of Dōkan, many retainers, beginning with Ōta Sukeyasu, abandoned the Ōgigayatsu clan and sought refuge in the territory of Akisada, leaving Sadamasa in a difficult situation. Only Dōkan’s military strategist, Saitō Kaga-no-kami, remained with Sadamasa and Sadamasa relied heavily upon his for support. Tensions rose between the Ōgigayatsu and Yamauchi families. In 1488, an attack by Akisada served as the opening chapter of the Chōkyō Conflict. Meanwhile, Miura Takahira, Sadamasa’s older brother of a different mother, took steps with the aim of becoming the next head of the Ōgigayatsu family.
Sadamasa responded by allying with Nagao Kageharu and entering into an alliance with his arch-rival, Ashikaga Shigeuji, the Koga kubō, to mount a resistance. Demonstrating his military prowess, Sadamasa prevailed with a small force in a series of battles. On 2/5 of Chōkyō 2 (1487), at the Battle of Sanemakihara, Akisada and Uesugi Norifusa (Akisada’s adopted son) approached the main base of the Ōgigayatsu in Kasuya in Sagami. Akisada captured the stronghold of Nanasawa to the north of Kasuya and then violently clashed against Sadamasa’s forces at Sanemakihara to the south of the castle. This was followed by another victory for Sadamasa in the sixth month at the Battle of Sugayahara in Musashi Province.
At the Battle of Takamihara, in anticipation of an attack by the Ōgigayatsu forces, Akisada requested reinforcements from his father, Uesugi Fusasada (the military governor of Echigo Province) and prepared to intercept the Ōgigayatsu at Takamihara on the district border of Hiki and Ōsato near Akisada’s base at Hachigata Castle in Musashi. This army was comprised of over 3,000 soldiers. The battle occurred at nighttime. The Ōgigayatsu forces executed their attack just as the Yamauchi forces rested after arriving at the site. Owing to Sadamasa’s skillful tactics, the Ōgigayatsu prevailed despite a deficiency in numbers, causing the Yamauchi to flee to Hachigata Castle.
This greatly raised the spirits of the forces. Sadamasa boasted that, within the next five years, the bushō in Kōzuke, Musashi, and Sagami provinces will be under my command. However, the power of the Ōgigayatsu family was limited solely to support from the Yamauchi family (who served as the deputy shōgun of the Kantō) and members of their family. After a series of battles, the forces grew fatigued and gradually declined in power.
There is a letter from Sadamasa dating from around 1489 addressed to a senior retainer named Soga Sukeshige that ties together Akisada’s impropriety and his own difficulties. Later, Sadamasa engaged in acts belittling of the Koga kubō so that, in the end, the alliance unraveled. Some retainers who viewed this as a result of Sadamasa’s arrogance betrayed the Ōgigayatsu in favor of the Koga kubō. A senior retainer, Ōmori Ujiyori, reproached Sadamasa and recommended settling with Akisada and the Koga kubō, but Sadamasa declined and continued to fight against the Yamauchi family.
In 1493, Sadamasa invaded Izu Province and expelled Ashikaga Chachamaru (Masatomo’s son), the Horigoe kubō. Sadamasa served as a guide for the invasion of Izu by Ise Sōzui (Hōjō Sōun) and formed an alliance with him. In 1494, Ōmori Ujiyori and Miura Tokitaka, both senior retainers of the Ōgigayatsu, died one after another. In the tenth month, Sadamasa deployed with Sōzui to Takamihara in Musashi Province and confronted Akisada, but Sadamasa suddenly died of illness. Under another theory, he died after falling from his horse will attempting to traverse the Ara River. There is a legend that the ghost of Ōta Dōkan caused Sadamasa to fall from his horse. The Teishō Temple in Nagaoka is said to be the family temple.
The deaths of three commanders, Uesugi Sadamasa, Ōmori Ujiyori, and Miura Tokitaka, represented a significant loss for the Ōgigayatsu family. Sadamasa’s nephew and adopted son, Uesugi Tomoyoshi, inherited the family but was subject to an invasion by Ise Sōzui (Hōjō Sōun) and his son, Hōjō Ujitsuna, leading to a gradual loss of the territory held by the Ōgigayatsu.