The Kasai-Ōsaki Uprising occurred in 1590 as a rebellion led by former retainers of the Kasai and Ōsaki clans against new landowners, Kimura Yoshikiyo and Kimura Kiyohisa (father and son). This occurred as a consequence of the Oushū Retribution, a set of measures taken by the Toyotomi administration with respect to the Tōhoku Region that resulted in the loss of castles and territory by designated clans who held grievances toward Toyotomi Hideyoshi. The role of Date Masamune in instigating the uprising was subject to detailed inquiry during and after the uprising, resulting in punitive measures by Hideyoshi.
The Kasai and Ōsaki clans were sengoku daimyō in the middle area of Mutsu Province. However, from the era of Date Tanemune (the great-grandfather of Date Masamune), were subordinate to the Date clan and were not in a position to send troops on their own accord in support of Hideyoshi’s campaign against the Gohōjō clan in Odawara.
On 7/26 of Tenshō 18 (1590), owing to the failure of Kasai Harunobu and Ōsaka Yoshitaka to participate in the campaign, Hideyoshi seized their territories and assigned their former territory comprised of thirteen districts (Isawa, Esashi, Iwai, Kesen, Motoyoshi, Tome, Monō, Oshika, Kurihara, Tōda, Shida, Tamatsukuri, and Kami) to Kimura Yoshikiyo. Yoshikiyo took over the former base of the Kasai at Teraike Castle, while his son, Kiyohisa, moved into the base of the Ōsaki clan at Myōu Castle. Yoshikiyo and Kiyohisa set about governing their newly assigned territories but were met with strong opposition from the former retainers of the Kasai and Ōsaki. After implementation of the measures comprising the Oushū Retribution, Asano Nagayoshi departed. Soon thereafter, in the middle of the tenth month, a dispute arose over the issue of transportation levies in territory governed by the Kimura (Yonaizumi in the Kami District of Mutsu). This was public opposition by as many as 100 individuals toward the established levies and appeared to have signs of an uprising.
Course of events
Outbreak of uprisings (Tenshō 18)
On 10/16, at Iwatesawa Castle, retainers of the former lord, Ujiie Yoshitsugu, joined with local residents to launch a revolt, and after occupying the castle, the uprising spread across the entire territory. Kiyohisa headed toward Teraike Castle to consult with his father in regard to their response. Afterwards, on the way back to Myōu Castle, he stopped by at Sanuma Castle and was then surrounded by ikki forces. Yoshikiyo came to his aid only to be locked down with all of the others in the castle. As a result, the ikki forces recaptured Teraike and Myōu castles from the Kimura and called the Kimura territory the ikki landholding.
En route to the capital, Asano Nagamasa received the news of this situation while staying at the Shirokawa Castle, whereupon he returned to Nihonmatsu Castle and ordered Gamō Ujisato and Date Masamune to rescue Yoshikyo and Kiyohisa. On 10/26, Ujisato and Masamune met in Shimokusa Castle in the Kurokawa District of the Date-controlled territory and agreed, beginning on 11/16, to jointly suppress the uprising. However, on 11/15, one day before the plans were to be executed, a retainer of Masamune named Suda Hōki (who was in Ujisato’s camp) alleged that Masamune had incited the uprising, while Masamune’s secretary named Sone Shirōnosuke brought-out a secret letter that Masamune had given to the ikki forces. Moreover, there was a report that the arquebuses discharged by Masamune’s infantry had no bullets. Consequently, on 11/16, Ujisato occupied Myōu Castle with only his own forces, and holed-up to prepare for the ikki and Masamune. He then dispatched a messenger to provide an update to Hideyoshi. Upon receiving the news, Hideyoshi sent Ishida Mitsunari and ordered him to devise a response.
Masamune also began to take steps on his own, attacking Takashimizu and Miyazawa castles. On 11/24, he toppled Sanuma Castle, rescued Yoshikiyo and Kiyohisa, and delivered both of them to Ujisato in Myōu Castle. Following the rescue of the Kimura, Ujisato halted preparations for a potential attack by Masamune and decided to hole-up in Myōu to pass the new year. To secure his return home, he demanded hostages from Masamune to which Masamune responded by tendering two senior retainers, Data Shigezane and Kokubun Morishige. Meanwhile, around this time, Ōsaki Yoshitaka (the former landowner), traveled to Kyōto to apologize to Hideyoshi for not participating in the Odawara campaign and to request the return of his territory. On 12/7, after the completion of a land survey, allocated one-third of the former territory to Yoshitaka and issued a license allowing the Ōsaki clan to return to their land.
Masamune summons and suppression (Tenshō 19)
On 1/1 of Tenshō 19 (1591), Ujisato, together with the hostages from Masamune, departed Myōu Castle to return to Aizu. On 1/10, Mitsunari arrived in the territory of the Sōma clan and notified Masamune of a request from Hideyoshi to come to Kyōto, whereupon he returned along with Ujisato and the Kimura to the capital. On 2/4, Masamune was subject to an inquiry in Kyōto. Masamune asserted that the secret letter produced as evidence that he instigated the uprising was fabricated, and that, in his own letters, the eye of the longclaw bird in his seal has a hole pierced with a needle. Hideyoshi accepted his defense and, once again, ordered Masamune to suppress the uprising, in addition to ordering Toyotomi Hidetsugu and Tokugawa Ieyasu to join as reinforcements.
In the fifth month, Masamune returned to Yonezawa in Dewa, then, on 6/14, he deployed for the purpose of subduing the uprising in earnest. However, he ran into stiff opposition from the ikki forces, including the successive loss in battle of senior retainers such as Hamada Kagetaka and Satō Tamenobu. On 7/4, after the fall of Teraike Castle, the remaining ikki forces surrendered and the uprising finally came to an end. On 8/14, Masamune summoned the leaders of the uprising to Mount Sue and ordered Izumida Shigemitsu and Yashiro Kageyori to slay all of them. On 12/7, he ordered Baba Sadashige and Baba Yorishige (father and son) of the Akiu clan to kill Nagae Katsukage, the lord of Ono Castle (an older brother in law of Kasai Harunobu and Sōma Yoshitane).
Kimura Yoshikiyo, the recently appointed landowner, was found to bear responsibility for the uprising and removed from his position. Yoshikiyo then turned to Ujisato to serve as a guest commander. The thirteen former districts of the Kasai and Ōsaki managed by the Kimura were granted to Masamune so the license given to Ōsaki Yoshitake in the prior year was scrapped and the Ōsaki were not restored as a daimyō family. On 9/23, after orders from Hideyoshi to conduct land surveys of the thirteen districts in Kasai and Ōsaki and to renovate the castles and fortresses, Ieyasu transferred the territory to Masamune. Masamune changed the name of Iwatesawa Castle to Iwadeyama Castle, and, in 1601, constructed and moved to Aoba Castle (later known as Sendai Castle) as his base.
Participation by Masamune in the uprisings
With respect to the suspicions regarding actions by Masamune to instigate the uprising such as by sending letters to the ikki, there were factors to deny his participation (a plot by Ujisato, false accusations by Suda Hōki, or propaganda by the ikki), but the view that Masamune himself instigated the uprising had the most credence. The Oushū Restribution resulted in the seizure of Aizu and eight districts that Masamure had acquired after the order issued by Toyotomi Hideyoshi for provincial daimyō to cease fighting one another over personal and territorial matters. As a means to recover his lost territory, it was viewed that Masamune stirred the uprising to oust the recently-appointed Kimura, and, based on recognition for suppressing the uprising, sought to acquire the former territory of the Kasai and Ōsaki. The killing of leaders of the uprising on Mount Sue was regarded as a means to destroy the evidence of his plot.
Despite outwardly recognizing Masamune’s explanations, Hideyoshi clearly imposed punitive measures based on his conclusion that the instigation of Masamune was a reason for the uprising.
Aftermath and consequences
Hideyoshi granted the thirteen districts of Kasai and Ōsaki to Masamune totaling 300,000 koku, but, in lieu of this grant, he seized six districts (Okitama, Shinobu, Date, Adachi, Tamura, and Katta) totaling 440,000 koku out of the twelve districts totaling 720,000 koku that comprised his fief. He then awarded this territory to Ujisato. As a consequence, Masamune’s fief amounted to nineteen districts totaling 580,000 koku.
The thirteen districts of Kasai and Ōsaki newly granted to Masamune had been severely ravaged by the uprising. Meanwhile, owing to the loss of the districts of Date, Shinobu and Okitama that had been part of the Date territory for over 200 years, the actual economic loss greatly exceeded the reduction in the fief of 140,000 koku. Moreover, it was not until 1626, after completion of the reconstruction work on the Kitakami River by Kawamura Shigeyoshi that the thirteen districts of Kasai and Ōsaki could be restored and the actual yield of the Sendai domain totaled 1,000,000 koku.
At the same time that Masamune was forced to relocate, the fief of the Date family was reorganized. Owing to reductions in the fief, the rice yield was lower across the board. Further, the newly granted sites were comprised of wilderness or valleys without the prospect for yielding crops. This led to dissatisfaction among the retainers of the Date family who faced difficult circumstances. Awano Shigekuni, the lord of Kitame Castle, refused to relocate and, as a consequence, was attacked and ousted from his castle. Senior retainers including Dare Shigezane, Kokubun Morishige, Oniniwa Tsunamoto, and Endō Munenobu fled one after another. The restoration of territory had been wholly delegated to senior retainers who had been granted expansive fiefs. This was a reason for a substantial decentralization of authority and why the system of local fiefs in the Sendai domain persisted until the end of the Edo period.