First Battle of Kōnodai

第一次国府台合戦

Ashikaga Clan

Shimōsa Province

Hōjō Clan

Date:  Tenth month of Tenbun 7 (1538)

Location:  Sagamidai in the environs of Kōnodai Castle in Shimōsa Province

Synopsis:  In this era, several members of the Ashikaga family wielded power over certain areas of the Kantō.  Ashikaga Yoshiaki (the Oyumi kubō) opposed Ashikaga Masauji (the Koga kubō) and aimed to occupy Kamakura (or, under another theory, Sekiyado Castle).  Overconfident and dismissive of the advice of his subordinates, Yoshiaki allowed opposing forces from the Hōjō army to cross the Edo River before engaging in battle.  This allowed the greater number of Hōjō forces to overcome and defeat Yoshiaki’s army and eliminate Yoshiaki himself.

Lord:  Ashikaga Yoshiaki 

Commanders:  Ashikaga Yoshiaki, Satomi Yoshitaka, Mariyatsu Nobumasa

Forces:  12,000

Losses:  Ashikaga Yoshiaki, Ashikaga Motoyori, Ashikaga Yoshizumi, others

Lord:  Hōjō Ujitsuna

Commanders:  Hōjō Ujitsuna, Hōjō Ujiyasu, Hōjō Nagatsuna (Genan)

Forces:  18,000

Losses:  Unknown

The First Battle of Kōnodai occurred in the tenth month of Tenbun 7 (1538) in Sagamidai in the environs of Kōnodai Castle in Shimōsa Province.  The conflict was waged between the army of Ashikaga Yoshiaki (the Oyumi kubō) and the Hōjō army.

Background

Kōnodai Castle is deemed to have originally been built by Ōta Dōkan when aiming to eliminate Makuwari Yasutane during the split of the Chiba clan.  Thereafter, it served as a gateway to Shimōsa Province and as a bridgehead when attacking Musashi Province from the direction of Awa, Kazusa, or Shimōsa provinces (collectively known as Bōsō); however, it had low value as a location for managing political affairs.

After a falling out between Ashikaga Masauji (the Koga kubō) and his son, Ashikaga Takamoto, Takamoto’s younger brother, Kūzen, returned to secular life and adopted the name of Ashikaga Yoshiaki.  From Takayanagi in Shimōsa, Yoshiaki was welcomed by Mariyatsu Nobukiyo (the fifth head of the Mariyatsu-Takeda clan in Kazusa Province) to Oyumi Castle in Shimōsa.  (Stories that Yoshiaki was wandering in the Tōhoku region are without any factual basis.)

Yoshiaki, with the backing of the Mariyatsu clan, in addition to the Satomi clan and others, was called the Oyumi kubō.  He opposed the Koga kubō and the Chiba clan and aimed to occupy Kamakura.  Hōjō Ujitsuna then came to prominence and occupied Kamakura and Edo Castle in Musashi Province, causing tensions in the relationship with Yoshiaki.  At this time, however, the Ōgigayatsu-Uesugi clan remained the biggest rival to Ujitsuna.  Yoshiaki had an alliance with the Ōgigayatsu-Uesugi and, in 1527, after he reconciled with Ujitsuna, the Mariyatsu followed after the Satomi to obey Yoshiaki, while even the Chiba clan who were formerly opposed to Yoshiaki came to support him.  Later, Yoshiaki intervened in internal conflicts in the Satomi and Mariyatsu clans and temporarily placed the entire region surrounding Edo Bay under this control.  After Yoshiaki demonstrated this degree of offensive action, he and Ujitsuna cleaved into opposing camps.

Nevertheless, Ujitsuna continued to place a priority on fighting the Ōgigayatsu-Uesugi so his relationship with Yoshiaki ebbed and flowed between conflict and reconciliation.  This was a similar situation for the Chiba, the Mariyatsu, and the Satomi clans.  Amidst these circumstances, Satomi Yoshitaka continued cooperation with Hōjō Ujitsuna who supported him when he inherited the headship of the clan.  In the sixth month of 1537, an internal conflict in the Mariyatsu clan reignited, and Ujitsuna sheltered Mariyatsu Nobutaka (the illegitimate eldest son of Nobuyasu) whom Yoshiaki drove into exile.  In the seventh month, the toppling of Kawagoe Castle (the base of the Ōgigayatsu-Uesugi clan) laid bare to Yoshiaki the threat posed by the Hōjō clan.  In the twelfth month, Chiba Masatane defected from Yoshiaki.  In the second month of 1538, after Ujitsuna attacked Kasai Castle on the border of Musashi and Shimōsa provinces, Yoshiaki supported the Ōgigayatsu-Uesugi forces defending the site, bringing to a head the conflict between Ujitsuna and Yoshiaki.  Meanwhile, Ashikaga Haruuji (the Koga kubō and Yoshiaki’s nephew) allied with Ujitsuna in opposition to Yoshiaki and the Yamanouchi-Uesugi family.  The Chiba clan followed suit.  This prompted Satomi Yoshitaka to part ways with Ujitsuna and align with Yoshiaki.

As an outcome of these developments, Yoshiaki decided to engage in battle against Ujitsuna.  In the tenth month of 1538, Yoshiaki led 10,000 soldiers including Satomi Yoshitaka and Mariyatsu Nobumasa and entered Kōnodai Castle.  Ujitsuna led 20,000 soldiers including his lineal heir, Hōjō Ujiyasu, and younger brother, Hōjō Nagatsuna, and entered Edo Castle.

Course of events

At a war council, the Oyumi army agreed to traverse the Edo River to attack the Hōjō army.  Overconfident of the stature of his family and his military prowess, Yoshiaki declared “As a member of the Ashikaga shōgun family, there is no one who would in earnest attempt to engage in battle against me.”  He then deployed and said he would kill any enemies who land on our shore, dismissing the assertion of Satomi Yoshitaka that they should decimate the enemy forces during their attempt to cross the river.  The prospect of waiting until the enemy completed their crossing caused Yoshitaka to doubt whether they would win the ensuing battle. Rather than trying to support Yoshiaki in a losing battle, he contemplated allowing Yoshiaki to die in the ensuing clash and then take advantage of the vacuum left behind to expand his own power.  Instead of heading toward the main battlefield at Matsudo, he moved his formation on the pretext of preparing for a pincer attack from the side of Ichikawa on a back road that would allow for a retreat.

On 10/7, upon the recommendation of a military tactician named Negoro Kinsekisai (Ōfuji Nobumoto), after crossing the river, the Hōjō army went via Matsudo Castle and clashed with the Oyumi army in Sagamidai to the north of Kōnodai.  In the early stages, the Oyumi army had the upper hand but the greater number of Hōjō forces gradually pushed back.  After receiving news that his younger brother, Ashikaga Motoyori and son, Ashikaga Yoshizumi, were killed in action, Yoshiaki became enraged and attempted to charge the Hōjō army himself.  He was then shot by arrows launched by archers in the Hōjō army and died.  Upon learning that Yoshiaki had been killed, Satomi Yoshitaka left the battlefield without clashing with the enemy forces and the Oyumi army collapsed.  Riding the momentum of their victory, the Hōjō army took control of Oyumi Castle, followed by Mariyatsu Castle.  After forcing the surrender of Mariyatsu Nobumasa, the Hōjō had Nobumasa’s brother of a different mother, Mariyatsu Nobutaka, resume his position as the lord of Mariyatsu Castle.

Aftermath

As a result of this battle, the authority of the Hōjō clan extended into Shimōsa Province.  Meanwhile, owing to the death in battle of Yoshiaki and restoration of Mariyatsu Nobutaka as the lord of Mariyatsu Castle, the territories controlled by the respective parties changed significantly.  The death in battle of Yoshiaki anticipated by Yoshitaka created a power vacuum allowing him to advance into the southern portion of Kazusa Province.  After occupying Kururi and Ōtaki castles under the command of the Mariyatsu clan, Yoshitaka took control of a majority of the Bōsō Peninsula.

The disposition of the territory under the direct jurisdiction of the Koga kubō (formerly held by Yoshiaki) became the subject of a dispute between Hōjō Ujiyasu (the successor to Hōjō Ujitsuna) and Ashikaga Haruuji.  There is a theory that this was the reason why Haruuji opposed the Hōjō clan at the Siege of Kawagoe Castle in 1546.

Theories regarding the target

According to a recent theory, the ultimate target of attack by Yoshiaki was not Kamakura but rather Sekiyado Castle in Shimōsa Province.  This is based on a letter from Ashikaga Yoshiaki to Uesugi Norimasa, the deputy shōgun of the Kantō, dated in the sixth month of 1538 (four months before this First Battle of Kōnodai).  At the time, Sekiyado Castle was in a vital location in northern Shimōsa for both marine commerce and land transport.  In addition, it was the most important auxiliary castle of the Koga kubō.  For Yoshiaki, who asserted himself as the legitimate Koga kubō, the control of Sekiyado Castle was essential to occupy the base of the Koga kubō at Koga palace.  In fact, since entering Oyumi Castle, Yoshiaki frequently referred to his intention to capture Sekiyado Castle in discussions with Satomi Yoshimichi (the uncle of Yoshitaka) and other senior members of his faction.

The shortest route from Oyumi to Sekiyado was from Motosakura Castle via the Inba lowlands and Hitachi River.  Motosakura Castle was located in the main territory of the Chiba clan who were connected to the Koga kubō and resisted Yoshiaki.  Moreover, the Chiba forced the surrender of the Usui clan who were in Yoshiaki’s camp, posing a difficult situation.  It is surmised that Yoshiaki then planned to occupy Kōnodai on the periphery of the area under the influence of the Chiba clan, and, from there, go upstream the Edo River to capture Sekiyado Castle.  In the sixth month of 1538, Yoshiaki issued a document promising to officially recognize the rights of the Kubō Temple to their temple lands located near Kōnodai.  Therefore, he may have been planning in advance to secure Kōnodai.  The Hōjō clan, who had taken control of the territory up to Kasai Castle on the opposite shore of the river from Kōnodai, could not accept these steps by Yoshiaki and, in with the intention of halting his plans, engaged in this First Battle of Kōnodai.

Based on another theory, the target was Kasai Castle which had fallen to the Hōjō shortly before the battle.  The reasoning is similar to the theory of Sekiyado Castle as the target.  For Yoshiaki to capture Sekiyado Castle as well as the Koga palace preceding it, Kasai Castle served as an important relay point in the lower reaches of the Tone River.  Moreover, the severing by the Hōjō of the route from Iwatsuki Castle to Kasai Castle to Oyumi Castle that was essential to coordinate with the Ōgigayatsu-Uesugi family (and the Yamanouchi-Uesugi family on the other side) had a major strategic impact on Yoshiaki.  Therefore, this First Battle of Kōnodai may have been an effort to recapture Kasai Castle and thereby secure the routes to Iwatsuki and in the direction of Sekiyado and Koga.