The Oyumi kubō was one of the families associated with the Ashikaga-Moto clan exercising the authority of the shōgun in the Kantō Region. Originating from the lineage of the Koga kubō, Ashikaga Yoshiaki rapidly gained power in a single generation, rivaling the main branch of the Ashikaga family for control of the Kantō. The title was derived from Yoshiaki’s base at Oyumi Castle in the Chiba District of Shimōsa Province. The role continued over two generations, first under Yoshiaki, then Ashikaga Yorizumi. In the Edo Period, this administration served as the basis for the Kitsuregawa domain.
The rise of Ashikaga Yoshiaki
The Kamakura kubō family, an ancestor of the Koga kubō family, had governed the Kantō from the time of Ashikaga Motouji, the son of Ashikaga Takauji. Gradually, however, the Kamakura kubō family became a rival of the main branch of the Ashikaga family (the shōgun family based in Kyōto in the lineage of Ashikaga Yoshiakira) vying for the status as the shōgun family of the Kantō. Finally, in the era of Ashikaga Motouji, the fourth Kamakura kubō, the family clashed militarily with Ashikaga Yoshinori, the sixth shōgun, in an event known as the Eikyō Conflict in 1438. After suffering a defeat, Motouji was forced to take his own life, upon which the Kamakura kubō was temporarily vanquished. Many of Motouji’s surviving children were subsequently killed by Yoshinori at the Battle of Yūki. After the assassination of Yoshinori in the Kakitsu Disturbance, support arose to revitalize the Kamakura kubō, whereupon Ashikaga Shigeuji, one of Motouji’s surviving children, became the next Kamakura kubō.
After coming of age, Shigeuji later confronted the bakufu and the Uesugi clan who served as the deputy shōgun in Kantō, but, at the inception of the Kyōtoku Conflict which ran from 1455 to 1483, Shigeuji was forced to abandon Kamakura. In 1455, he established a base at Koga Castle in Shimōsa Province, from where he exercised power independently and was thereafter referred to as the Koga kubō. Following his death, the Koga kubō family experienced frequent internal conflict, including a confrontation between Ashikaga Masauji (the second Koga kubō) and his son, Ashikaga Takamoto (the third Koga kubō) in an event known as the Eishō Conflict.
Takamoto had a younger brother who served as a monk under the name of Kōnen. Kōnen later became associated with a cadet family of the Kai-Takeda clan called the Mariyatsu-Takeda based in Kazusa Province. Takeda Nobunaga, the second son of Takeda Nobumitsu, served as a retainer of Ashikaga Shigeuji, the Koga kubō. Upon orders of Shigeuji, Nobunaga invaded Kazusa and seized the territory of the Uesugi clan who were the deputy shōgun of the Kantō. This enabled the Mariyatsu-Takeda to become a sengoku daimyō family in Kazusa. The fifth head of the Mariyatsu clan, Mariyatsu Nobuyasu, desired to subjugate the Kantō, but there were other influential clans in the area, including the Yūki and the Chiba, closely aligned with the Koga kubō, relegating the Mariyatsu to a subordinate position.
In the early part of the Eishō era (1504-1521), Nobuyasu had Kōnen return to secular life and adopt the name of Ashikaga Yoshiaki. He received him at Oyumi Castle in Shimōsa and installed him as the Oyumi kubō. Nobuyasu had Yoshiaki serve as a puppet ruler while he exercised the real power. On the pretext that Yoshiaki was a member of the Ashikaga clan, Nobuyasu expanded his influence across the Kantō Region. The Mariyatsu clan witnessed the peak of its prosperity during this period while the Oyumi kubō served as a nominal administration on behalf of the clan.
Yoshiaki, however, was not the type of individual to silently serve as a puppet for others. The Satomi clan of Awa, the Usui clan of Shimōsa (a relative of the Chiba family), and the Oda clan of Hitachi Province approached Yoshiaki in an attempt to leverage his authority by offering military resources. Meanwhile, the Chōnan-Takeda clan, relatives of the Mariyatsu, were threatened by the expansion of power by the Mariyatsu, causing them to approach the Koga kubō. The stature of Yoshiaki as a noble spread beyond the expectations of the Mariyatsu, and in a letter from Yoshiaki to Satomi Yoshimichi, he expressed his ambition to control Motosakura Castle (the home base of the Chiba clan) and Sekiyado Castle (the most significant auxiliary castle of the Koga kubō).
The peak years and demise of the Oyumi kubō
In these circumstances the Gohōjō, a powerful clan in control of Izu and Sagami provinces, entered the scene and came into conflict with the Oyumi kubō. Initially, the Mariyatsu and Oyumi kubō explored a possible alliance with the Gohōjō, so conflict was not inevitable. The relationship changed when, in 1524, the Gohōjō occupied Edo Castle and took complete control of the western shore of Tōkyō Bay. As opposed to the Koga kubō which had its base inland, the Oyumi kubō, the Mariyatsu, and the Satomi clans who controlled the eastern shore of Tōkyō Bay, became fearful of the military power of the Gohōjō who were capable of seizing control of maritime rights in the bay. This caused them to confront the Gohōjō. Meanwhile, an alignment of interests between the Koga kubō, who sought to expel Yoshiaki, and the Gohōjō, who aimed to control Tōkyō Bay, led them to forge an alliance.
In 1533, the Satomi clan witnessed an internal rebellion known as the Tenbun Rebellion, or, alternatively, as the Inamura Incident. This event originated from the assassination of Satomi Sanetaka at Inamura Castle. Acting upon orders of Mariyatsu Nobukiyo, Yoshiaki lent support to Satomi Yoshitoyo of the Oyumi faction, but the faction disintegrated after Yoshitoyo was killed by Satomi Yoshitaka. This led to a confrontation between Yoshiaki and Nobukiyo. After prevailing, Yoshiaki had Nobukiyo enter the priesthood and forced him to retire. In 1534, Nobukiyo died. Eventually, after a succession dispute arose between siblings within the Mariyatsu clan, Mariyatsu Nobutaka and Mariyatsu Nobumasa, Yoshiaki brought Satomi Yoshitaka into his faction in support of Nobumasa and expelled Nobutaka, adeptly intervening in the troubled affairs of the Mariyatsu. In this way, Yoshiaki elevated himself above the role of a puppet ruler, emerging as the formal Oyumi kubō. He then confronted the Koga kubō from his same family as well as the Gohōjō. On the basis of the Oyumi kubō family serve to unify the daimyō of southern Kantō, Yoshiaki quickly expanded his influence in the region.
Nevertheless, the rapid rise to prominence of the Oyumi kubō family raised fears among the Gohōjō clan and the Koga kubō family, resulting in an alliance between the two parties. In a bid to prevent the combination of the Koga kubō and Gohōjō clan, in 1538, Yoshiaki led an army comprised of daimyō from Awa, Kazusa, and Shimōsa, including Mariyatsu Nobumasa and Satomi Yoshitaka, and committed to a final showdown against the allied forces of Hōjō Ujitsuna and Ashikaga Haruuji, an event known as the First Battle of Kōnodai.
A skilled tactician, Yoshiaki led his forces from the frontline, engaging in ferocious combat. His forces initially pushed back the Hōjō and Ashikaga armies, but the Satomi forces were not very cooperative because Yoshitaka was not, from the onset, invested in the fight. Meanwhile, some of the members of the Mariyatsu held Yoshiaki in contempt owing to his earlier intervention in their succession struggle, and the low morale of the forces led to their collapse in the face of counterattacks by the Hōjō army. Yoshiaki himself died in battle. Following his demise, Oyumi Castle was recaptured by the Chiba clan who enjoyed the support of the Hōjō. The surviving members of the Yoshiaki’s family depended upon the Satomi to flee to Awa, resulting in the end of the Oyumi kubō.
The end of the Oyumi kubō enabled the Hōjō clan to solidify its hegemony in the southern Kantō. Moreover, the death of Yoshiaki gave way to a resurgence of the succession struggle in the Mariyatsu family between Nobumasa and Nobutaka. This led to a rapid deterioration of the family’s fortunes and an attack by the Satomi clan, after which the family served as retainers for Hōjō Ujiyasu.
Among the surviving members of Yoshiaki’s family, his eldest daughter, Shōgakuni, served as a nun at the Taihei Temple in Kamakura; however, she later became the formal wife of Satomi Yoshihiro, the eldest son of Satomi Yoshitaka, after his earnest appeals for her hand in marriage. Consequently, many of Yoshiaki’s former retainers came to serve the Satomi clan.
The eldest son of Yoshiaki, Ashikaga Yoshizumi, was killed along with his father at the Battle of Kōnodai. After the death of Yoshiaki, his second son, Ashikaga Yorizumi, grew-up under the protection of the Satomi. Thereafter, he roamed several provinces, whereupon his daughter became a mistress of Toyotomi Hideyoshi, the most powerful leader in Japan at the time. In 1590, after the start of the Odawara Expedition, Yorizumi leveraged the support of the Satomi clan to defeat the Chiba clan, recaptured Oyumi Castle, and, for a period of several months, revived the position of the Oyumi kubō. After the demise of the Hōjō clan, Yorizumi’s eldest son, Ashikaga Kunitomo, was allowed, through the devices of Hideyoshi, to wed Ashikaga Ujihime (the daughter of Ashikaga Yoshiuji, the last Koga kubō). Yoshiaki’s lineage survived through the Kitsuregawa clan.
In the Edo period, Tokugawa Ieyasu, who valued the traditions of the Ashikaga clan that served as the shōgun family, awarded Kitsuregawa Yoriuji the status of a family with a fief of 100,000 koku even though his production was 4,500 koku. The Kitsuregawa domain continued thereafter. The family enjoyed special recognition although rice production was less than 10,000 koku.