History Uesugi Zenshū's Rebellion (上杉禅秀の乱)

Although the rebellion lasted only a few months, it exposed the increasingly fragile relationship between the Muromachi shogunate in Kyōto and the Kamakura administration in eastern Japan. Its aftermath deepened divisions within the Ashikaga family, weakened one branch of the Uesugi clan, and contributed to the chain of conflicts that eventually culminated in the Eikyō Rebellion of 1438.

Background

During the Muromachi period, political authority in Japan was effectively divided between Kyoto and Kamakura. The Muromachi shogunate governed from Kyōto, while eastern Japan was administered by the Kamakura Kubō, a branch of the Ashikaga family established to oversee the Kantō region. The Kamakura Kubō was assisted by the Kantō Kanrei, a hereditary office monopolised by the Uesugi clan after the Kō brothers' decline during the Kannō Disturbance.

The balance of power became unstable after the death of the third Kamakura Kubō, Ashikaga Mitsukane (足利満兼, 1378–1409). His twelve-year-old son Ashikaga Mochiuji succeeded him in 1409. Initially, Uesugi Norisada (上杉憲定, d. 1411) of the Yamanouchi Uesugi branch served as Kantō Kanrei. Still, after his removal in 1411, the office passed to Uesugi Ujinori of the rival Inukake Uesugi branch.

As Mochiuji was still young, Ujinori sought to strengthen his own influence. He aligned himself with Mochiuji's uncle, Ashikaga Mitsutaka (足利満隆, d. 1417), and Mitsutaka's adopted son, Ashikaga Mochinaka (足利持仲, d. 1417), who was also Mochiuji's younger brother. Together, they attempted to dominate the Kamakura government and reduce the young Kubō's authority.

Relations steadily deteriorated. In 1415, a dispute at the Kamakura council led to Ujinori's dismissal as Kantō Kanrei. He was replaced by Uesugi Norimoto (上杉憲基, d. 1417) of the Yamanouchi branch, the son of the former Kanrei Norisada. The decision intensified the long-standing rivalry between the Inukake and Yamanouchi branches of the Uesugi clan.

Another source of resentment was the confiscation of land belonging to one of the Inukake branch's retainers. Ujinori regarded this as a direct challenge to his authority and resigned his office in protest. His dismissal, combined with political rivalries within both the Uesugi and Ashikaga families, set the stage for open rebellion.

Outbreak of the rebellion

In the autumn of 1416, Ujinori organised a broad coalition against Mochiuji. His supporters included Ashikaga Mitsutaka and Mochinaka, as well as many powerful eastern lords such as Iwamatsu Mitsuzumi (岩松満純, d. 1417), Chiba Kanetane (千葉兼胤), Takeda Nobumitsu (武田信満, d. 1417), Oda Mochiie (小田持家), Yūki Mitsutomo (結城満朝), Ashina Morimasa (蘆名盛政), Nasu Sukeyuki (那須資之), Nagao Ujiharu (長尾氏春), Ōjō Mitsumoto (大掾満幹), Yamairi Yoriyoshi (山入与義), together with numerous provincial warriors and local landholders across eastern Japan.

Many of these families had grown dissatisfied with the Kamakura administration or maintained close personal and marriage ties with Ujinori. Contemporary sources suggest that nearly half of the major military houses of eastern and northern Japan offered him some degree of support.

On the night of 2 October 1416 (Ōei 23), Mitsutaka launched the uprising from Hōjuin Temple near the Kamakura residence of the Kubō. Ujinori advanced to seize Ashikaga Mochiuji and Uesugi Norimoto before they could organise resistance. The attack caught Kamakura by surprise. Although defenders under Miura Takaaki (三浦高明) attempted to hold Kewaizaka Pass, confusion spread through the city, allowing Mochiuji to escape with a handful of retainers.

After first reaching Norimoto's residence, Mochiuji fled west through the mountains before eventually taking refuge with Imagawa Norimasa (今川範政, d. 1420), the military governor of Suruga Province. Ujinori and Mitsutaka, meanwhile, occupied Kamakura and effectively took control of the city. Mitsutaka proclaimed himself the new Kamakura Kubō and appealed to warriors throughout the Kantō and northern provinces for support.

The shogunate intervenes

News of the uprising reached Kyōto on 13 October. Initial reports incorrectly claimed that both Mochiuji and Norimoto had been killed, causing considerable alarm at the Muromachi court. Shōgun Ashikaga Yoshimochi (足利義持, 1386–1428) was temporarily absent on pilgrimage, and senior officials gathered to assess the rapidly changing situation.

Once reliable information confirmed that Mochiuji had escaped and was requesting assistance from Suruga, Yoshimochi convened a council of leading daimyō. Acting partly on the advice of his uncle Ashikaga Mitsuakira (足利満詮, d. 1417), the shōgun decided to support the Kamakura Kubō.

The decision was not based solely on loyalty to Mochiuji. Even before the rebellion, relations between Kyoto and Kamakura had been strained, and the shogunate regarded Mochiuji as increasingly independent and difficult to control. Nevertheless, an armed revolt led by a former Kantō Kanrei posed a direct threat to the established political order. More significantly, evidence emerged that Yoshimochi's younger brother Ashikaga Yoshitsugu (足利義嗣, 1394–1418), who harboured ambitions of becoming shōgun himself, had secretly maintained contacts with Ujinori. The possibility that the rebellion might merge with a conspiracy against the shogunate transformed what had appeared to be a regional conflict into a matter of national importance.

Yoshimochi, therefore, ordered military intervention. Forces led by Imagawa Norimasa, Uesugi Fusakata (上杉房方, d. 1423), Ogasawara Masayasu (小笠原政康), Utsunomiya Mochitsuna (宇都宮持綱), members of the Satake clan and other loyal commanders advanced towards Kamakura in support of Mochiuji.

Defeat of the rebels

As government armies approached, the balance of power shifted rapidly. Ujinori attempted to strike Suruga in the hope of eliminating Mochiuji before reinforcements arrived, but the Imagawa defeated his forces. At the same time, warriors from Musashi Province, including the Edo clan and the Toshima clan, turned against him under pressure from advancing government forces.

On New Year's Day of 1417, Ujinori won a temporary success at the Battle of Seya Plain, defeating a combined Edo-Toshima force. The victory proved short-lived. While his army was engaged elsewhere, Imagawa troops crossed into Sagami Province and advanced towards Kamakura.

By 10 January 1417, government forces had surrounded the city. Ujinori, Mitsutaka, and Mochinaka withdrew to the monks' quarters associated with Tsurugaoka Hachimangū in Yukinoshita, Kamakura. There, facing certain defeat, they committed suicide. According to some traditions, Ujinori took his own life after retreating to one of the temple lodgings known as the Nijūgo-bō (二十五坊, "the twenty-five temple quarters").

The rebellion collapsed with their deaths. The Inukake branch of the Uesugi clan effectively lost its political position in the Kantō. However, some of Ujinori's sons survived by entering the Buddhist clergy under the shogunate's protection. Other rebel leaders met similar fates. Takeda Nobumitsu was pursued back to Kai Province, where he committed suicide, while Iwamatsu Mitsuzumi was captured and executed.

Consequences

Although the rebellion had been suppressed, its political consequences were profound. Within Kyōto, investigations into Ashikaga Yoshitsugu's involvement led to a wider purge. Yoshitsugu fled the capital but was captured, confined to a monastery, and later killed in 1418. Reports produced during the investigation implicated several leading military governors and court nobles in an alleged conspiracy with Ujinori. Several prominent figures were dismissed, exiled or placed under house arrest. However, some historians regard these accusations as part of an internal struggle for influence within the shogunate rather than evidence of a genuine conspiracy.

In Kamakura, Ashikaga Mochiuji recovered his position but emerged more suspicious and independent than before. Rather than seeking reconciliation, he spent the following years pursuing Ujinori's former supporters. Families, including the Oda, Takeda, and other eastern warrior houses, faced repeated attacks. Some provincial lords stopped attending the Kamakura government altogether, fearing retaliation. Ujinori's former retainers in Kazusa Province even organised an uprising of their own shortly after his death.

Ironically, the shogunate had never been an enthusiastic supporter of Mochiuji. Its intervention had been motivated primarily by the need to preserve political stability and prevent Ujinori's rebellion from merging with wider opposition centred on Ashikaga Yoshitsugu. The fact that Ujinori's surviving sons received protection from Kyōto suggests that the shogunate was already preparing for potential conflict with Mochiuji.

The relationship between Kyōto and Kamakura continued to deteriorate after 1417. Mochiuji increasingly asserted his independence, while the shogunate took measures to limit his authority, including transferring certain territories associated with the Ashikaga family to direct shogunal control and rewarding regional lords who had supported the campaign against Ujinori.

The conflict also affected northern Japan. Ashikaga Mitsunao (足利満直, d. 1438), the Shinohara Kubō established in Mutsu Province, had initially sympathised with Ujinori and Mitsutaka but refrained from joining the rebellion after Yoshimochi ordered eastern warriors to support Mochiuji. Following the war, relations between Mitsunao and Kamakura deteriorated further, encouraging his gradual political alignment with Kyoto rather than the Kamakura government.

Historical significance

Uesugi Zenshū's Rebellion marked a turning point in the history of the Muromachi state. It exposed the weaknesses of the dual system of government centred on Kyōto and Kamakura, highlighted rivalries within both the Ashikaga and Uesugi families, and reflected broader changes in eastern Japanese society, including the growing independence of provincial warrior bands and local leagues.

Although the rebellion itself lasted only four months, it intensified the long-running conflict between the Muromachi shogunate and the Kamakura Kubō. The mistrust generated by the war continued to shape politics in eastern Japan for decades, contributing directly to the Eikyō Rebellion (1438) and the Yūki Campaign (1440), which finally brought an end to the Kamakura branch of the Ashikaga family.

References:

• Hall, John Whitney (ed.), The Cambridge History of Japan, Vol. 3: Medieval Japan, Cambridge University Press, 1990.
• Sansom, George, A History of Japan, 1334–1615, Stanford University Press, 1961.
• Berry, Mary Elizabeth, The Culture of Civil War in Kyoto, University of California Press, 1994.
• Japan Knowledge (ed.), Sekai Daihyakka Jiten (世界大百科事典), entry "Uesugi Zenshū no Ran" (上杉禅秀の乱).
• Yamakawa Shuppansha (ed.), Nihonshi Shōjiten (日本史小辞典), revised edition, Yamakawa Shuppansha, 2016.
• Kokushi Daijiten Henshū Iinkai (ed.), Kokushi Daijiten (国史大辞典), Yoshikawa Kōbunkan.