The Battle of Ogawadai occurred in Tenshō 6 (1578) in Hitachi Province.  The conflict was waged by the Hōjō clan led by Hōjō Ujimasa and an alliance of opposition forces to the Hōjō led by Satake Yoshishige.  This event is also referred to as the Battle of Hitachi-Ogawadai.

Fierce attacks by the Hōjō

From the first month of 1574, Hōjō Ujiyasu intensified attacks on Sekiyado Castle in Shimōsa Province.  Uesugi Kenshin traversed the Mikuni Pass in the second and eighth months to provide reinforcements while Satake Yoshishige endeavored to dampen the progress of the Hōjō.

At the end of the eleventh month, Kenshin and Yoshishige split over differences in how to respond to the Hōjō army.  Yoshishige, via Yūki Harutomo, received support from Takeda Katsuyori to facilitate a settlement whereas Kenshin maintained his focus on invading Shimōsa, Kōzuke, and northern Musashi provinces.  The consequences of Kenshin’s split from the Satake clan were significant.  Harutomo severed relations with Kenshin and aligned with the Hōjō.  Through the offices of Yoshishige, Yanada Mochisuke gave-up the resistance on the sixteenth and opened the castle on the nineteenth.  Meanwhile, Yoshishige and Utsunomiya Hirotsuna settled with Hōjō Ujimasa and withdrew.

In the sixth month of 1575, Ujimasa aimed to conquer Shimotsuke so he sent Hōjō Ujiteru to invade the province and topple Enomoto Castle.  Riding the momentum, the Hōjō army attacked the main base of Oyama Hidetsuna, cornering him just as the castle was about to fall.  Owing to concerns about the situation, in the eleventh month of 1574, Yoshishige broke relations and restored his alliance with Kenshin.  Kenshin also focused on the threat to the Oyama clan and demanded that Yoshishige support Hidetsuna.

Meanwhile, in the eighth month of 1575, the Hōjō suppressed the Kazusa-Sakai clan (who were aligned with the Satomi) and provided support to Masaki Taneshige and Toki Tameyori.  In the ninth month, Yura Narishige and Yura Kunishige (father and son) revitalized Goranda Castle in Kōzuke Province and prepared defenses against Numata Castle aligned with the Uesugi, engaging in frequent clashes.  In the tenth monh, Kenshin traversed the Mikuni Pass to invade the Kantō, trampling upon the territory governed by the Yura clan in the course of imposing a major blow but the main base of the Yura clan at Kaneyama Castle and Goranda Castle were not captured.  Moreover, Kenshin’s forces did not advance to Shimotsuke or Musashi provinces and, without containment of the Hōjō army attacking the Oyama and Satomi clans, in the eleventh month, he brought his forces back to Echigo.  As a result, in the twelfth month, Oyama Castle fell and Hidetsuna fled for the protection of the Satake clan.  In the second month of 1576, Ujimasa ordered Ujiteru to reinforce Oyama Castle and had it completed in the fifth month.

In the fifth month of 1576, Kenshin traversed the Mikuni Pass into the Kantō for the last time, decimating Nitta, Ashikaga, and Kiryū, but could not topple the Hōjō.  That winter, unable to endure the offensive by the Hōjō, the Kazusa-Sakai clan proposed a settlement, making clear the superior position of the Hōjō in the Bōsō (the three provinces of Awa, Kazusa, and Kōzuke in the Kantō).

In view of the circumstances, Masaki Noritoki, Satomi Yoshihiro, and Kajiwara Masakage pleaded one after another with Kenshin to come to the Kantō for support, but he did not come.  Instead, he devoted his attention to the war against the Oda after allying with the Hongan Temple (Ikkō-ikki forces).  He responded to the Satake that, once his strategy for Noto and Etchū took root, he would return again to the Kantō but that opportunity did not arise.

Defection by Yūki Harutomo

In the sixth month of 1577, just when the invasion of northern Kantō by the Hōjō was proceeding on course, Yūki Harutomo was lured by his older brother, Oyama Hidetsuna, to join forces with Kenshin and Yoshishige, making clear his opposition to the Hōjō.  Ujimasa quickly dispatched Ujiteru and Ujikuni and, in the seventh month, attacked Yūki Castle.  Harutomo fiercely resisted the attack but was defeated outside of the castle by the vanguard forces of the Hōjō, resulting in several hundred troops killed.  Attacks by the Hōjō army continued beyond the end of the eighth month.  On 8/28, the two armies clashed at Yamakawaguchi in the Yūki District.  On this occasion, the Hōjō army gained the upper hand but was unable to compel the surrender of Harutomo.

Nevertheless, Utsunomiya Hirotsuna requested to become subordinate to the Hōjō.  Once Yoshishige learned that Harutomo was attacked by the Hōjō army, he attempted to assault the primary bases of the Hōjō at Enomoto and Oyama castles.  Having detected these plans, in parallel with attacking the Yūki, Ujimasa dispatched Sakai Yasuharu to Kondō Tsunahide at Enomoto Castle.  Ujimasu informed Yasuharu that Yoshishige would definitely launch an assault so he should advise Tsunahide to bolster his defenses accordingly.  In the ninth month, the Satake army invaded Shimotsuke to mount an attack on Oyama Castle, directing the attention of the Hōjō army to Shimotsuke.

From 10/9 to 10/19, Ujiteru and Ujikuni allocated fiefs in Shimotsuke so, by this time, Yoshishige had his forces cease operations while the Hōjō secured Enomoto and Oyama.  Meanwhile, the Satake achieved their original objective to support Harutomo.

Settlement between the Satomi and Hōjō clans

While Ujiteru and Ujikuni clashed with the Yūki and Satake clans, Ujimasa deployed from Odawara Castle and entered Edo Castle, and then onward toward Sekiyado.  Ujimasa’s target of attack was not the northern Kantō but rather the Satomi clan.  In the ninth month, after Ujimasa invaded from eastern Kazusa and Hōjō Ujichika from western Kazusa, on 9/30, Takeda Toyonobu of the Kazusa-Takeda clan capitulated.

In the tenth month, Satomi Yoshihiro proposed a settlement whereupon Ujimasa’s second daughter, Ryūjuin, wed Yoshihiro’s lineal heir, Satomi Yoshiyori, forging through marriage a political alliance between the two clans.  This is known as the Bōsō Alliance, an alliance between the Satomi clan of Awa Province and the Hōjō clan of Sagami Province.

In response to urgent requests from Oda Ujiharu, Ujimasa headed-out to capture Ujiharu’s former main base of Oda Castle, defended by Kajiwara Masakage.  After applying pressure again to the Yūki clan, however, he returned to base.

Revival of the opposition to the Hōjō by Utsunomiya Hirotsuna

Concerned by the situation, in the twelfth month of 1577, Harutomo dispatched Mizunoya Katsutoshi to Utsunomiya Hirotsuna.  He then adopted Hirotsuna’s second son, Tomokatsu (later known as Yūki Tomokatsu), severed ties with the Hōjō, and reverted to the anti-Hōjō alliance.  Further, Harutomo had his younger sister wed Edo Shigemichi under the command of Satake Yoshishige (the older brother of Tomokatsu’s mother).

In a bid to counter these actions, on 1/25 of Tenshō 6 (1578), Ujimasa commenced negotiations with Date Terumune.  On 2/23, Ujimasa exchanged written pledges with Ashina Moritaka for a pincer attack against the Satake.  He had already formed an alliance with Tamura Kiyoaki.  Having established a common front with the Ashina and Tamura clans, Ujimasa set the end of the fourth month for the attack against the Satake.

The Satake also continued to urgently request reinforcements from Kenshin.  In a letter dated 2/10 of Tenshō 6 (1578), Kenshin consented to advance his forces into the Kantō and to deploy in the fourth month.  On 3/13, however, Kenshin died of illness and the expedition by his forces to the Kantō was canceled.

Battle of Ogawadai

At the end of the fourth month of 1578, Satake Yoshishige, together with Yūki Harutomo and Nasu Suketane, commenced an attack against Mibu Yoshitake who was aligned with the Hōjō.  In response, Ujimasa advanced with earlier support into the territory of the Yūki and, beginning on 5/5, initiated assaults against Yūki and Yamakawa castles.  To reinforce the Mibu, the main division of Ujimasa entered Sekiyado Castle.  Upon hearing this news, Yoshishige suspended the capture of Mibu and instead headed toward Oyamaguchi in support of Harutomo.  On 5/21, Yoshishige, joined by forces led by Utsunomiya Hirotsuna, Haga Takatsugu, and Daijō Sukemoto, established a base at Ogawa-no-hara to the east of Yūki Castle and, on 5/28, at Ogawadai.

Meanwhile, Ujimasa departed from the Yamakawa base and built a fort in Takei and Tajima located in-between Yamakawa Castle and Yūki Castle, confronting the Satake clan across the Kinu River.

Around this time, a succession struggle erupted in the Uesugi clan between Kenshin’s adopted sons, Uesugi Kagetora and Uesugi Kagekatsu.  This is known as the Otate Conflict.  During this conflict, while maintaining his focus on Hitachi and Shimotsuke, Ujimasa requested Takeda Katsuyori to send reinforcements to Kagetora.

The Satake set-up a base in a stronghold and established robust formations.  Ujimasa could not achieve a quick outcome and, instead, witnessed the passage of time without meaningful progress.  Ujimasa expressed with sorrow to Yura Kunishige and Yura Narishige (father and son) that this was a once in a generation regret.  Finally, on 6/7, Ujimasa pulled back to Dotō-no-hara and, on 6/8, further retreated to Narusawa.

After confirming the withdrawal of Ujimasa, on 7/4, Satake Yoshishige pulled-up from Ogawadai to attack Mibu Castle, launching the assault the next day.  In the middle of the seventh month, he withdrew his forces.

Consequences

In this battle, all of the forces mobilized by Satake Yoshishige were allies in the Kantō.  This enabled a unified opposition to Ujimasa.  In the midst of Kenshin’s waning influence, the formation of a close alliance among the Satake family and their allies transformed the nature of the opposition to the Hōjō to comprise forces across the entire territory of the Kantō.

In the middle of the sixth month, Yoshishige, along with Yūki Harutomo, Utsunomiya Hirotsuna, and Nasu Suketane exchanged written pledges, forging a military alliance led by the Satake.  Following its formation, this alliance was referred to as the tōhō-no-shū, or the Group from the Eastern Region.

After Takeda Katsuyori restricted the main division of Hōjō Ujimasa, he deployed forces to Echigo.  The interference with Ujimasa’s forces caused a break in relations between the Hōjō and the Kai-Takeda, triggering the eventual collapse of the alliance between the two clans.  Despite the nature of the Battle of Ogawadai as a localized event, in the end, it gave rise to major developments in the Kantō of the Azuchi-Momoyama period.