Lifespan: Unknown to 2/26 of Tenbun 19 (1550)
Rank: shugo daimyō
Clan: Jōjō-Uesugi → Echigo Uesugi
Father: Uesugi Fusazane
Adoptive Father: Uesugi Fusayoshi (?)
Siblings: Sekisui-in (formal wife of Date Hisamune), Sadazane, Jōjō Sadanori, Sadaaki
Wives: [Formal] Daughter of Uesugi Fusayoshi, [Second] Daughter of Nagao Yoshikage
Children: Daughter (formal wife of Nagao Harukage), daughter (wife of Ashina clan), nephew (treated like a son), Date Sanemoto (intended for adoption but canceled)
Uesugi Sadazane served as a shugo daimyō during the Sengoku period. Sadazane was a military governor of Echigo Province and the eighth (and final) head of the Echigo-Uesugi family. He may have been adopted by Uesugi Fusayoshi but it is not confirmed. Uesugi Kenshin (known as Nagao Kagetora in his youth) was his nephew.
Sadazane was born to a branch of the Uesugi clan known as the Jōjō-Uesugi family. In the sixth month of 1503, he received the daughter of Uesugi Fusayoshi (the military governor of Echigo) as his formal wife and became Fusayoshi’s son-in-law.
In the eighth month of 1507, Nagao Tamekage, the deputy military governor and sengoku daimyō of Echigo, gave support to Sadazane to oust Fusayoshi. On 11/6 of 1508, Sadazane became the military governor but, in fact, was a puppet of Tamekage. Around this time, Sadazane wed the younger sister of Tamekage. His formal wife (Fusayoshi’s daughter) is believed to have died as of this time. Usami Fusatada presented Sadazane with a prized sword inscribed with the name of Usami Sadamitsu.
To avenge the removal of Fusayoshi from his position, Uesugi Akisada (the deputy shōgun for Kantō and older brother of Fusayoshi) invaded Echigo, whereupon, in 1509, Sadazane and Nagao Tamekage fled in defeat to neighboring Etchū Province. Having seen that Akisada’s army could not garner the support of the kokujin, or provincial landowners, in Echigo, on 4/20 of 1510, Tamekage and Sadazane traveled from Etchū via Sado Province by sea route to a harbor named Kanbara-no-tsu. With additional soldiers from Sado, Tamekage’s forces had regained their strength and defeated Akisada’s army in clashes across Echigo. While Akisada’s army attempted to retreat, Tamekage pursued them and one of the reinforcements named Takanashi Masamori killed Akisada, enabling victory for Tamekage’s army. In addition to the death of Akisada himself, Akisada’s army suffered a major defeat including the loss of Nagao Sadaaki and other commanders.
Gradually, however, Sadazane came to resent serving as a puppet for Tamekage. In 1513, he assembled forces comprised of Usami Fusatada and Fusami Sadamitsu (father and son) who were lineal retainers of the family of the military governor, Jōjō Sadanori from the main Jōjō clan (who was either a younger brother or nephew), and several clans from the Agakita group (kokujin from northern Echigo). He then occupied Kasugayama Castle to direct ongoing resistance, but failed and was temporarily incarcerated resulting in a loss of influence. Thereafter, Jōjō Sadanori and others came together again to oppose Tamekage, and, on 8/3 of 1536, forced Tamekage into retirement, but did not go so far as to enable Sadazane to grasp power. In any event, Tamekage’s successor, Nagao Harukage, could not attract wide support so Sadazane’s authority showed signs of being restored.
Around 1538, discussions were raised with Sadazane concerning adoption. Sadazane did not have a son, so plans were made with support of Nakajō Fujisuke (the lord of Tossaka Castle) and others for the adoption by Sadazane of Tokimunemaru (later known as Sanemoto) who was the son (Sadazane’s nephew) of a relative – Date Tanemune, a daimyō in Mutsu Province. The Date clan had connections to the Uesugi clan and to Echigo Province. Tokimunemaru’s grandmother on his father’s side hailed from the Uesugi, while his mother was the younger sister of Fujisuke. Tanemune viewed the proposed adoption as an opportunity to further expand his territory.
Nagao Tamekage also actively supported the proposal. To raise funds, on 10/24, special levies were imposed in the Kubiki District. In the ninth month of 1539, military forces from the Date clan invaded the territory of Honjō Fusanaga in the Koizumi manor of Agakita which faction opposed the adoption. This invited conflict between kokujin in the northern portions of Echigo and those under the command of the Uesugi in Dewa Province.
In the fourth month of 1542, Sadazane sent a written pledge to Nagao Harukage indicating his desire to enter the priesthood and urging to move forward with the adoption. In the sixth month, Harukage sent senior retainers, the Naoe and Tairako clans, to assist the Date clan. Prior to the adoption, Tokimunemaru received one of the characters in his name from Sadazane, and thereafter became known as Date Sanemoto. He also received a sword from a famous sword-maker named Usami Sadamitsu inscribed with a motif of the family crest of the Uesugi clan featuring a ring of bamboo surrounding sparrows, symbolizing a perfect match. Plans were made for Tokimunemaru to depart to Echigo on 6/23, but, on 6/20, internal discord known as the Tenbun Conflict arose within the Date clan so the adoption was canceled and Sadazane’s plans stalled.
At the end of the Tenbun era (1532 to 1555), Echigo was shaken by events including a revolt by Kuroda Hidetada. Harukage’s younger brother, Nagao Kagetora (later known as Uesugi Kenshin) suppressed the revolt causing surrounding individuals not to mention Sadazane himself to take note. In 1548, Sadazane intervened in a dispute between Harukage and Kagetora, endeavoring to support Kagetora.
In his later years, Sadazane entered the priesthood and adopted the name of Gensei. He died of illness in 1550. Owing to the absence of an heir, following his demise, the family of the military governor of Echigo came to an end. Upon orders of Ashikaga Yoshiteru (the thirteenth shōgun of the Muromachi bakufu), Kagetora became the military governor of Echigo in place of Sadazane.