The Oushū Retribution occurred during the seventh and eighth months of 1590 in which the administration of Toyotomi Hideyoshi reassigned territory across the Oushū Region, namely, in the northern provinces of Mutsu and Dewa. These actions further included the promotion as well as the demotion or removal of assorted daimyō in the region, setting the stage for uprisings by those who held grievances with respect to the new order imposed by the Toyotomi.
This activity began in 1585 when Toyotomi Hideyoshi sent Kanayama Muneara to promote stability (peace and reconciliation) in Ouu (Mutsu and Dewa). By 1588, Muneara traveled to Ouu three times for negotiations with all of the landowners. In the ninth month of 1588, Mogami Yoshiaki, followed by Date Masamune, pledged their allegiance to Hideyoshi, contributing significantly to stability in Ouu. In the first month of 1589, Hideyoshi sent a letter to Masamune requesting him to visit Kyōto in the first half of the year. However, instead, in the fifth month of 1589, Masamune invaded Aizu in the territory held by the Ashina clan. Owing to Masamune’s disregard of the request to visit Kyōto and breaking of the peace in Ouu, Hideyoshi distrusted him. Hideyoshi made clear that unless Masamune withdrew from Aizu, he would prepare to send troops to Ouu. In the eleventh month, the Hōjō clan overturned a decision by Hideyoshi concerning the territory of the Numata and invaded Nagurumi in the territory of the Sanada clan. The following spring, Hideyoshi then launched an expeditionary army to conquer the Hōjō in the eastern portion of the country.
In 1590, Hideyoshi joined Utsunomiya Kunitsuna of Shimotsuke Province and Satake Yoshishige of Hitachi Province for the Conquest of Odawara. On 7/11 of Tenshō 18 (1590), Odawara Castle was vacated while Hōjō Ujimasa and Hōjō Ujiteru (siblings) committed seppuku. Many other members of the family including Hōjō Ujinao were exiled to Mount Kōya. Consequently, the era of the Gohōjō as a sengoku daimyō family came to an end. Prior to these events, on 6/14, Gamō Ujisato had already arrived in Nihonmatsu in Mutsu Province, serving as the vanguard of the Toyotomi army in the Oushū Region.
On 7/17, Hideyoshi, together with Utsunomiya Kunitsuna and others, headed from Odawara toward Shimotsuke and, on 7/26, entered Utsunomiya Castle. Daimyō from the Kantō and Ouu regions also came to Utsunomiya, whereupon a reformation (reallocation of landholdings and the status of landowners) was carried out with respect to the daimyō from Ouu in an event known as the Utsunomiya Retribution. Prior to the arrival of Hideyoshi in Utsunomiya, Satake Yoshinobu of Hitachi and Nanbu Nobunao of the northern part of Mutsu came to Utsunomiya. On 7/27, Hideyoshi granted a license to Nobunao concerning seven districts in the Nanbu territory (Nukanobu, Hei, Kazuno, Kuji, Iwate, Shiwa, and the Tōno township). On 7/28, Date Masamune (who had participated in Odawara) came to Utsunomiya to welcome Hideyoshi to Oushū. On 8/1, he recognized the rights of Satake Yoshishige to Hitachi and territory of 540,000 koku. The prior year, the Date defeated the Ashina clan at the Battle of Suriagehara, amassing a territory of 1,500,000 koku in Ouu. However, in addition to arriving late to Odawara, by attacking the Ashina in Aizu, Masamune violated Hideyoshi’s order for daimyō to stop territorial and personal conflicts. As a result, Hideyoshi seized four districts in Aizu, the Iwase District, and the Asaka District. His fief was reduced to 13 districts totaling 720,000 koku in Mutsu and Dewa provinces.
With Masamune serving as his guide, Hideyoshi conducted a march accompanied by the Oushū Retribution army led by Gamō Ujisato (who had received Aizu in his fief) and Asano Nagamasa (a magistrate) to examine the progress of the reformation. In the course of this activity, he returned again to Utsunomiya but, on 8/6, with Masamune serving as the guide, the Oushū army arrived in Shirokawa. After repelling retainers of the Kasai clan who attempted to resist, on 8/9, the army entered Aizu-Kurokawa Castle. Thereafter, after the Hienuki clan was ousted from Toyagasaki Castle (later known as Hanamaki Castle), Nagamasa entered and then ordered commanders for the Oushū army to advance to the environs of Hiraizumi to suppress several castles in the territory of the Waga clan. Retainers of Nagamasa were stationed on behalf of the Toyotomi and progress was made toward establishing a new system. After conducting a land survey, district governors and officials remained while the Oushū army withdrew. This marked the completion of Hideyoshi’s unification of the country.
Notable actions taken by the Toyotomi administration in the Oushū Reformation included the following:
Removal from their positions: Ishikawa Akimitsu, Esashi Shigetsune, Kasai Harunobu, Ōsaki Yoshitaka, Waga Yoshitada, Hienuki Hirotada (Shigetsuna), Kurokawa Haruuji, Tamura Muneaki, and Shirokawa Yoshichika (for not serving in Odawara).
Reduction in fief: Akita Sanesue (a daimyō in northern Dewa – fief reduced 78,5000 koku to 52,440 koku), Onodera Yoshimichi (a daimyō and lord of Yokote Castle in Dewa – fief reduced by one-third to 31,600 koku). The fief of Date Masamune was reduced from 1,140,000 koku in 6 districts (notably including the Okitama, Shinobu, and Date districts) to 720,000 koku in 13 districts of territory abandoned in uprisings in Kasai and Ōsaki. In the year after this initial reduction, owing to concerns of his complicity in the Ōsaki-Kasai Uprising, his fief was further reduced to approximately 580,000 koku and he was transferred from Yonezawa Castle to Iwatesawa Castle (later known as Iwadeyama Castle). Around this time, Masamune received the Hashiba surname from Hideyoshi, and given that his base at Iwadeyama was in the former territory of the Ōsaki, adopted the title of Hashiba-Ōsaki Chamberlain.
Recognition of territorial rights: Mogami Yoshiaki, Sōma Yoshitane, Akita Sanesue, Tsugaru Tamenobu, Tozawa Mitsumori (Moriyasu), Nanbu Nobunao, and others.
Newly conferred fief: Gamō Ujisato (a retainer of the Toyotomi, he received a fief of 420,000 koku from the former territory of the Ashina clan, which, in the following year, was increased to 920,000 koku), Kimura Yoshikiyo (a retainer of the Toyotomi, he received a fief of 300,000 koku from the Kasai-Ōsaki centered on Teraike Castle in Tome, but, in the following year, was removed from his position owing to concerns of his complicity in the Ōsaki-Kasai Uprising).
After the Ouu region came under the governance of the Toyotomi administration, a land survey was performed to confirm the kokudaka, or rice yields, of local daimyō families, and, upon this basis, to impose military service requirements. Those daimyō in Ouu who received official recognition by the administration of their rights to landholdings leveraged their status as publicly recognized lords to strengthen the control over their respective families. This served as a catalyst to transform daimyō families such as the Date and Nanbu who had previously existed in an atmosphere governed by familial ties into modern daimyō. By means of the Oushū Retribution, Hideyoshi finally completed the work to unify the country.
However, the forced relocation by the Toyotomi administration of daimyō in the region bred significant dissatisfaction and friction among those involved. First, after the main force of the Toyotomi army withdrew from Oushū, the Kasai-Ōsaki Uprising broke out in the territory of the Kimura, led by former retainers of the Kasai and Ōsaki clans who had been removed from their positions of power. As though acting in concert with this action, the Waga-Hieinuki Uprising and the Iwasaki Uprising occurred on the former territory of the Waga and Hienuki, the Senboku Uprising occurred in the Senboku area of Dewa, and the Fujishima Uprising occurred in the Shōnai area of Dewa.
Based on the reformation, Kunohe Masazane, who had been on a comparable level to Nanbu Nobunao within the Nanbu clan, became dissatisfied at being treated as a retainer of Nobunao, resulting in an armed clash with Nobunao in an event known as the Revolt of Kunohe Masazane. To suppress the uprisings and conflicts arising in the wake of the reformation, in 1591, the Toyotomi administration was compelled to send a large army to the region.
Meanwhile, after having received official recognition of the rights to his landholdings, in looking back on the Oushū Retribution years later, Akita Sanesue noted that one-hundred years prior, Dewa and Mutsu were divided among the Shōnai, the Mogami, the Nanbu, the Akita, the Senboku, and the Tsugaru, while the landowners did not get along well and were continuously engaged in fighting one another. However, owing to Toyotomi Hideyoshi, the country was unified and became peaceful, and owing to the reformation, the war situation in the Tōhoku Region was finally resolved.