The Eishō Conflict was a series of battles across the Kantō and Hokuriku regions that occurred in Eishō era (1504 to 1521) during the early part of the Sengoku period and are summarily referred to as the Eishō Conflict.
The Eishō Conflict can generally be understood in the context of four interrelated problems. Each one was caused for separate reasons. Nevertheless, underlying the conflict was the killing of Uesugi Fusayoshi on 8/7 of 1507. Nagao Tamekage launched a rebellion that led to discord in Echigo Province. Fusayoshi then ordered Tamekage’s father, Nagao Yoshikage (the deputy military governor of Echigo), to support Jinbō Yoshimune, but owing to betrayal by Yoshimune, Fusayoshi was killed in an event known as the Battle of Hannyano.
The other related problems included: (i) the unanticipated death in battle of Uesugi Akisada, the deputy shōgun of Kantō during the conflict in Echigo that triggered an internal struggle in the Yamauchi-Uesugi family; (ii) a difference of opinions between Ashikaga Masauji the Koga kubō and his son regarding how to respond reignited internal conflicts, and (iii) after the clashes in Echigo drew to a close, efforts by Nagao Tamekage to eliminate the Jinbō clan as a means to tighten control over the province.
Conflict in Echigo Province
In the ninth month of 1506, Nagao Yoshikage, the deputy military governor of Echigo, died in battle in Etchū Province. His eldest son, Nagao Tamekage, became the next head of the Nagao clan and deputy military governor of Echigo. In the eighth month of 1507, Tamekage backed Uesugi Sadazane in a sudden attack against Uesugi Fusayoshi, the military governor of Echigo. Fusayoshi relied upon Uesugi Akisada, the deputy shōgun of Kantō, in an attempt to flee to the Kantō, but Tamekage cornered him at the Amamizu Pass where, together with Maruyama Nobuzumi, Fusayoshi killed himself.
In 1509, Akisada raised a large army to seek revenge for the death of Fusayoshi. Knowing that he was outnumbered, Tamekage fled to Sado Province. In 1510, he traveled from the village of Teradomari to land again in Echigo. After the supporters of Tamekage went on a counteroffensive, Nagao Fusanaga, lord of Sakado Castle, did not allow the Uesugi army to enter the castle and had them stay at Rokumanki Castle on a steep hill. When Tamekage’s forces approached Rokumanki Castle, the Uesugi army withdrew, but with the help of reinforcements led by Takanashi Masamori (Tamekage’s maternal grandfather), killed Akisada at the Battle of Nagamorihara. Subordinates of Akisada including Nagao Sadaaki and Takayama Norishige were also killed, resulting in a major decline in the capabilities of the Yamauchi-Uesugi family.
Thereafter, Tamekage defeated other enemy forces including Usami Fusatada, Irobe Masanaga, Honjō Tokinaga, and Takenomata Kiyotsuna, leading to the demise of the Jinbō clan of Etchū.
Internal conflicts in the Yamauchi-Uesugi family
Following the death in battle of Akisada, Uesugi Norifusa, retreated from Shiroi Castle in Kōzuke after having initially stationed at the castle for the purpose of eliminating Akisada and Tamekage. Uesugi Akizane, the adopted son of Akisada, succeeded him as the deputy shōgun of Kantō. However, Uesugi Norifusa, who was also adopted, took issue with this plan and, with the support of Yokose Kageshige and Nagao Kagenaga, disputed the succession. Akizane requested the aid of his older brother, Ashikaga Masauji (the Koga kubō) but Norifusa allied with Ashikaga Takamoto (the son of Masauji and nephew of Akizane) to resist. By bringing the Koga kubō into the dispute, the Kantō became divided. Uesugi Tomoyoshi, the head of the Ōgigayatsu-Uesugi family attempted to mediate, but failed while Ise Sōzui invaded Sagami Province.
In 1512, Akizane received support from Nagao Akikata and Narita Akiyasu and headquartered at Hachigata Castle in Musashi Province, but lost in an attack by Yokose Kageshige and Nagao Kagenaga. Having lost his seat as the head of the Yamauchi-Uesugi family, he relied upon his older brother, Masauji, to flee to Koga Castle.
In 1515, the death of Akizane brought about the demise of the Yamauchi-Uesugi family. Norifusa succeeded to the role of the deputy shōgun of Kantō, while the role of head of house affairs transferred from Akikata of the Sōja-Nagao family to Kagenaga of the Ashikaga-Nagao family. The Yamauchi-Uesugi family that had been weakened by this internal conflict invited disaffection again from Nagao Kageharu, who fought against Uesugi Tomooki (the nephew of Tomoyoshi), Hōjō Ujitsuna of the Hōjō clan of Sagami Province, and Takeda Nobutora of the Takeda clan of Kai Province.
Internal disputes in the family of the Koga kubō
Ashikaga Masauji (the Koga kubō) and his eldest son, Ashikaga Takauji (later known as Ashikaga Takamoto) competed for the role of the Koga kubō. In a confrontation in 1510, the two settled through the mediation of Akisada, but, in 1511, the two clashed again in regard to succession to the Yamauchi-Uesugi family after the death of Akisada. Masauji was joined by Iwaki Tsunetaka and Iwaki Yoshitaka (father and son), Satake Yoshikiyo, and Oyama Shigenaga, while Takamoto aligned with Utsunomiya Shigetsuna and Utsunomiya Tadatsuna (father and son) and Yūki Masatomo, triggering battles across the Kantō. In addition, Masauji’s second son, Ashikaga Yoshiaki, became independent as the Oyumi kubō in Shimōsa Province.
This internal dispute had a close relationship with a dispute in the Shimotsuke-Utsunomiya clan known as the Eishō Discord. There were also expectations of backing of the Koga kubō by Utsunomiya Shigetsuna, who corresponded to the father-in-law of Takamoto. As a result, Takamoto assumed office as the third Koga kubō with the backing of Shigetsuna. Moreover, a conspicuous number of political marriages were arranged between Shigetsuna and the clans who supported Takamoto, including the Yūki, the Ue-Nasu clan, and the Oda clan. Takamoto himself received the daughter of Shigetsuna, Zuiunin, as his formal wife.
In 1519, Takamoto had Masauji enter the priesthood, whereupon Masauji retired at the Kuki residence in Musashi Province, drawing the conflict to a close. This, however, led to the decline of the Koga kubō family, while the Gohōjō clan steadily advanced in the Kantō.
Conquest of the Jinbō clan of Etchū Province
In 1521, Nagao Tamekage joined Hatakeyama Yoshifusa, the military governor of Noto Province, to attack and eliminate Jinbō Yoshimune, who was responsible for the death of Tamekage’s father, Nagao Yoshikage. This is known as the Eishō Conflict of Etchū.