was a daimyō of the Yamagata Domain in Dewa Province, in the late Sengoku and early Edo periods. He was known as the "Fox of Dewa".
His younger sister, Yoshihime, later became the wife of Date Terumune and gave birth to Masamune, making him the uncle of Date Masamune.
It was recorded in historical documents that his height was over 180 cm.
Biography Early life Mogami Yoshiaki was born on the first day of the first month of the Tenbun era (1546) to his father, Yoshimori, and his mother, Nagaura. His birth name was Hakujumaru and he succeeded his father as daimyō of Yamagata Prefecture. The Mogami clan which he hailed from has a prestigious bloodline that descended from the Shiba clan, a branch of Ashikaga clan, and the "Yoshi" character of his name "Yoshiaki" was bestowed directly by the 13th shogun, Ashikaga Yoshiteru. Furthermore, the Mogami clan was in the position as direct vassals of the Ashikaga shogunate. As a boy who was raised in a samurai and aristocratic clan, Yoshiaki had the literary ability to compose letters over three meters long and was able to enjoy renga in Kyoto alongside famous renga poets such as Satomura Shōha.
On June 14, 1563 (Eiroku 6), Yoshiaki, aged 17, and his father went to Kyoto to have an audience with Shogun Yoshiteru and present him with a horse and a sword.
In 1564, when his sister Yoshihime married Date Terumune, the Mogami clan became allied with the Date clan. At some point during this period, the Mogami clan underwent a succession conflict.
In 1570, at the age of 25, Yoshiaki inherited the clan leadership from his father and set upon his goal of reviving the hereditary position of his clan as Oshu Tandai (Overseer of Dewa Province, the areas of which encompass modern-day Akita and Yamagata prefectures). He expanded not only into the northern and western parts of Yamagata Prefecture, but also into the southern part of Akita Prefecture.
Due to the confusion over the succession of the Mogami clan, local lords in the Dewa Province, such as Tendo Yorisada, and his clan members Higashine Yorichage, Kaminoyama Mitsukane, and Shiratori Nagahisa, tried to become independent. Yoshiaki, who inherited the family headship, used fairly forceful methods to suppress their attempts to declare independence from the Mogami clan. Mogami had Kaminoyama's vassal Satomi Minbu betray and kill him. Mogami also had Yorichage's vassal Satomi Kageyori betray and kill him. Having destroyed the unity of the Tendo family, Yoshiaki exiled Tendo Yorisada's son Yorimizu, who had succeeded him after his death.
Unification of Dewa province
In 1571, Mogami Yoshiaki officially became the head of the Mogami clan. During this time, Yoshihime sent information about the Date clan to Yoshiaki, her and Yoshiaki's actions made the Date clan distrust the Mogami family. Yoshiaki fought against the Date clan twice in different years, 1574 and 1578, in both battles Yoshihime advanced to the middle of the battlefield to create a peace treaty. Yoshiaki married a woman from the Osaki clan of the Mutsu province, who was his relative. When Date later attacked the Osaki clan the relationship between Yoshimitsu and Date Masamune deteriorated.
In 1580, he got help from Satomi Minbu allowing him to successfully take over the Kaminoyama Castle which lead to Kaminoyama Mitsukane committing suicide.
In 1581, he expanded his power to Murayama District and took over Oguni Castle. Yoshiaki also attacked Sakenobe Castle and forced Sakenobe Hidetsuna to surrender. Later, Hidetsuna became Yoshiaki's chief vassal. In 1583, he expanded the Semboku areas, and threatened Daihōji Yoshiuji. Daihōji declared war against the Mogami clan as result. Later, Yoshiuji was defeated and committed suicide.
In 1584, Yoshiaki defeated the Sagae clan which was led by Sagae Takamoto who committed suicide. Yoshiaki then attacked the Tendo clan, who were based in Tendo, just north of Yamagata, into Kokubu (present-day Miyagi Prefecture), led by Tendō Yorizumi. Later, Yorizumi fled to the territory of Kokubun Morishige, causing the Tendō clan to collapse. Furthermore, he also defeated the Shiratori clan within the same area.
Meanwhile, in Dewa Province, one of the remaining local lords in conflict with Yoshiaki was Nagahisa Shiratori. Nagahisa Shiratori's territory was in Murayama County, Dewa Province, near present-day Murayama, Yamagata. He was an obstacle to Yoshiaki, who was trying to pacify Dewa, but he also had connections with Oda Nobunaga and was plotting to obtain the title of Dewa no Kami (Lord of Dewa). Yoshiaki, who had read of these developments, invited Shiratori Nagahisa to his castle, Yamagata Castle, in 1584, claiming to be seriously ill. According to the "Tale of Mogami Yoshiaki" written in the early Edo period, Yoshiaki, who was bedridden, asked Shiratori Nagahisa to "serve as guardian until my eldest son, Yoshiyasu, comes of age," and handed him a family tree that had been passed down from his ancestors. It is recorded that when Shiratori Nagahisa was about to receive the family tree document, Yoshiaki suddenly killed him with a sword that he had hidden. With the elimination of Nagahisa, the Mogami clan finally asserted their dominance of the region. It was reported that the assassination of Nagahisa was ordered by Oda Nobunaga several years prior, before the Honnō-ji Incident in 1582, when Nagahisa enraged Nobunaga by lying to Nobunaga claiming that he was the ruler of Dewa province.
In 1586, Yoshiaki fought against Onodera Yoshimichi. Yoshiaki's eldest son, Mogami Yoshiyasu and Tateoka Mitsushige succeeded in defeating the Onodera reinforcements. In October, Yoshiaki crossed the Rokuji Highway and invaded Shōnai in an effort to reinforce Tōzenji Yoshinaga, lord of Tozenji Castle, against the attack of his enemy, Daihōji Yoshioki. Yoshioki was defeated in battle the same month and committed suicide, causing the Daihōji clan to go extinct. In 1587, he succeeded in taking control of Shonai (western Yamagata prefecture). However, the next year, his army was defeated and routed by Honjō Shigenaga, a retainer of Uesugi Kagekatsu, in Battle of Jugorihara. This defeat, along with the fact that his nephew, Date Masamune, was also expanding his own ambitions at the same time, and he was targeting domains within the Mogami clan, prompted Yoshiaki to give up Shōnai and move his focus towards the Date clan. Conflict with Date Masamune In 1588, an internal conflict broke out within the Osaki clan, the former Oshu Tandai, protector of Oshu region, with the Mogami and Date clans, who had each requested reinforcements, entered into a state of war. This conflict was brought to a peace agreement through the desperate pleas of his younger sister, Yoshihime, but while they were distracted by the conflict with the Date clan, Honjo Shigenaga, a subordinate of the Uesugi clan from Echigo Province, took over Shonai. In response to this, Yoshiaki sought to recapture the region from the Uesugi clan. However, when Toyotomi Hideyoshi came to power In 1590, he forbade any private wars among daimyo or feudal lords in Japan. Yoshiaki then submitted to Hideyoshi's authority. In the same year, Yoshiaki was given about 200,000 koku by Toyotomi Hideyoshi.
In 1589, on May, Tokugawa Ieyasu sent a letter to Katakura Kagetsuna, imploring him that Date Masamune reconcile with Yoshiaki.
Incident of Yoshiaki daughter In 1591, after the Siege of Odawara, he participated in the Kunohe Rebellion. During this time, Toyotomi Hidetsugu, who had been chosen as Toyotomi Hideyoshi's successor, fell in love with Yoshiaki's daughter, Komahime, and married her, and Yoshiaki became an important Toyotomi daimyo as because of his relation to the Toyotomi clan. In 1591, Yoshiaki was allowed to use the surname of Toyotomi, and usually called himself Hashiba Yoshiaki. Although he did not end up sailing to Korea during the Bunroku Invasion, in 1592, he went to Nagoya Castle in Hizen with 500 of his retainers to prepare for passage to Korea.
In July 1595, an incident occurred which involved his daughter, who had been betrothed to Hidetsugu. This incident was triggered by the birth of Hideyori, a male heir, to Hideyoshi's second wife Yodo-dono. This resulted in Hidetsugu being accused of treason and forced to commit seppuku at Mount Kōya on the order of Hideyoshi, presumably to secure the inheritance of Hideyori. Besides Hidetsugu, Hideyoshi also killed Hidetsugu's wife, concubines, and children, who were also executed at Sanjogawara. Yoshiaki's daughter, Komahime, who was only 15 years old had recently married Hidetsugu, was also executed as a result. Yoshiaki begged for her life but was refused. Komahime was beheaded along with Hidetsugu's other wives and concubines, and her body was dumped in the Sanjogawara River on August 2 of the same year. Furthermore, Yoshiaki was suspected of participating in Hidetsugu's rebellion, but he was pardoned with the assistance of Tokugawa Ieyasu's intercession on his behalf. As result of the execution of Komahime, Yoshiaki's wife Osaki-dono was struck with deep grief by the sudden death of her daughter, and she died on August 16. After this incident, Yoshiaki grew closer to Ieyasu and became his strongest supporter.
In 1597, Yoshiaki's son Yoshiyasu was eventually given the official title of Shūri-daifū as the eldest son of the Mogami family.
Sekigahara Campaign
In 1600, when the Sekigahara campaign broke out between Ieyasu and his enemies led by Ishida Mitsunari, Ieyasu entrusted Yoshiaki with command of northern Oshu. On April 19, Ieyasu instructed the Nanbu, Onodera, and Akita clans to obey Yoshiaki's command, after Ieyasu turned his army back to face Mitsunari's forces on July 25, while he was at Oyama (Oyama City, Tochigi Prefecture). Yoshiaki was also informed by Ieyasu that the campaign against the Uesugi clan was cancelled. As a result, the troops that had gathered in Oshu returned to their home provinces. The Uesugi clan became emboldened and began to actively work against Ieyasu, contacting Yoshiaki and others to encourage them to join the Uesugi side.
Mogami faced a dilemma because he still supported Ieyasu, but if he did not join the Toyotomi side, there was a high possibility that he would be attacked by the Uesugi. As Yoshiaki believed in Ieyasu's victory in the Kamigata region, he tried to buy time, but in the end, the Uesugi forces invaded the Mogami territory on September 8. Yoshimichi Onodera, who was based at Yokote Castle (present-day Yokote City, Akita Prefecture), also responded to the Uesugi and invaded the Mogami territory. This resulted with now the Mogami clan withstand the invasion of battled Uesugi Kagekatsu.
The Uesugi forces which numbered more than 20,000, were invaded from the south by the main force commanded by Naoe Kanetsugu via the Kitsunegoe Highway, and from the west by the Shonai area. Because the difference in military strength between the Mogami forces and the Uesugi forces were huge, Yoshiaki requested reinforcements from Date Masamune. The message was relayed through Yoshiaki's eldest son, Yoshiyasu. Masamune decided to send reinforcements out of obligation for his mother, Yoshihime, who was a sister of Yoshiaki, and also loyalty to Ieyasu. In the same campaign, Yoshiaki aided in Date's siege of Shiroishi, and was then attacked in his own home castle of Hataya and Kaminoyama. He used geographical advantages to resist the invasions. Yoshiaki concentrated his forces in Hasedō Castle, Yamagata Castle, and Kaminoyama Castle. Naoe Kanetsugu's forces launched an all-out attack on Hasedō Castle, which was defended by 1,000 men. with the cooperation of the reinforcements sent by Yoshiaki from Yamagata Castle and the soldiers of Hasedō Castle, and their high fighting spirit, the defenders of Hasedō Castle fought well.