Tenshō Mogami Conflict

天正最上の乱

Mogami Yoshimori

Dewa Province

Mogami Yoshiaki

Date:  Tenshō 2 (1574) 

Location:   The territory of the Mogami clan in Dewa Province

Synopsis:  Mogami Yoshimori, the tenth head of the clan, favored his second son, Nakano Yoshitoki, over his eldest son, Mogami Yoshiaki, to become his successor.  Nevertheless, after garnering control of the clan, Yoshiaki implemented harsh rule, alienating many of the kokujin, or provincial landowners, in the territory.  This led to conflict between the two sides across Dewa for a significant portion of Tenshō 2 (1574), pulling the Date and many other local clans into the fight.  In the end, the two settled and Yoshiaki turned his attention toward the unification of Dewa.

The Tenshō Mogami Conflict occurred in 1574 as an internal conflict of the Mogami clan, the sengoku daimyō of Dewa Province.  The conflict was waged between Mogami Yoshiaki and his retired father, Mogami Yoshimori, along with their respective supporters.

Prelude

In 1570, a dispute broke-out between Mogami Yoshimori (the tenth head of the Mogami clan), and Mogami Yoshiaki (his eldest son and designated heir).  Yoshimori adored his second son, Nakano Yoshitoki.  Yoshimori’s efforts to transfer headship of the clan to Yoshitoki are said to have precipitated the conflict.  Yoshimori gained the support of Date Terumune, a sengoku daimyō and the sixteenth head of the Date clan married to Yoshimori’s daughter.  The conflict began with skirmishes centered around the Yamagata Basin.  In the fifth month, a senior retainer of Yoshimori named Ujiie Sadanao persuaded the parties to settle.  In the eighth month, Yoshiaki inherited the headship of the clan and became the lord of Yamagata Castle.  At this time, Yoshiaki was twenty-four years old while his father, Yoshimori, was forty-nine.  The next year, Yoshimori entered the priesthood and adopted the name of Eirin.

After succeeding his father, Yoshiaki engaged in harsh governance of the provincial landowners and gōzoku, or families of wealth, in his territory.  Resistance to Yoshiaki’s governance led these landowners and families to call upon Yoshimori in an effort to oust Yoshiaki, reigniting tensions between father and son.  In the first month of 1574, Yoshimori sent a letter to Terumune to request reinforcements, whereupon, ten days later, Terumune dispatched forces to the Mogami territory.  Thus, clashes broke-out with the Date and Yoshimori on one side against Yoshiaki on the other.  This is known as the Tenshō Mogami Conflict.

Course of Events

On 1/25, after Koyanagawa Morimune, a retainer of the Date, attacked Kaminoyama Castle, Kaminoyama Mitsukane surrendered to the Date.  On 1/29, kokujin from the Murayama region who allied with the Date demonstrated their loyalty to Date Terumune by launching an assault against Sagae Kanehiro (an ally of Yoshiaki) at Sagae Castle.  At this time, Tendō Yorisada and Kurazō Yorizane (from illegitimate branches of the Mogami descended from the Satomi clan of the Seiwa-Genji), along with Shiratori Nagahisa (the lord of Yachi Castle), in addition to members of the Sagae clan including the Shiraiwa, the Mizonobe, and the Aterazawa aligned with the Date forces.  During the assault on Sagae Castle, the besieging forces penetrated to the second of three lines of moats and, on 2/2, Kanehiro surrendered.  According to one theory, the Sagae clan orginally supported Yoshimori but, owing to the attack by the Date forces, they were forced to fight back.

In this way, most of the kokujin in the Mogami territory allied with Yoshimori so Yoshiaki attempted to settle, but failed.  On 2/24, supporters of Yoshiaki attacked the Hōjō manor of the Date clan in Kawatoi of the Okitama District, defeating Memesawa Tango-no-kami among others.  On 2/28, Yoshiaki and Yoshimori settled, and Terumune was informed that prisoners from the battle at the Hōjō manor were released and the small contingent of Yoshiaki’s forces deployed to Narage withdrew.  On 3/28, however, Yoshiaki launched a surprise attack on the Hōjō manor from Kaminoyama, whereupon, on 4/15, Terumune attacked Hataya Castle in the Murayama District.  Next, on 4/22, he ordered forces from the districts of Date, Shinobu, Katta, and Shibata to engage in all-out war.  From 5/3 to 5/4, Yoshiaki fought against the Wakaki forces and, on 5/5, battled against Yoshimori and the Nakano clan at Emata.  On 5/7, Terumune went to Shinjuku in the Yashiro manor in the Okitama District and, on 5/11, deployed to Nakayama in the Hōjō manor, setting fire to the home village of Yoshiaki.  On 5/20, forces from each of the opposing sides wielding arquebuses engaged in a battle.  On 6/2, Yoshiaki’s forces launched a nighttime assault in Shinchi, burning down the encampment of the Shiroishi and Koori clans.  On 6/7, Terumune moved went to Hataya to attack the castle, but after receiving news that Ashina Morioki, his ally and a sengoku daimyō from Aizu in Mutsu, had died, he proceeded to attack Yanazawa Castle on 6/8 and then returned to Yonezawa on 6/9.  In the sixth month, the Sōma clan which had been opposed to the Date clan sent a letter to Yoshiaki to request his support.

Earlier, in the fourth month, Date Sanemoto, captured the auxiliary castle of Hatchōme in an attack on Nihonmatsu in Mutsu.  He then set his sights on Nihonmatsu Castle.  Seeking a settlement, the Nihonmatsu clan reached out in many directions, but, owing to the discovery in the sixth month of plotting by the Nihonmatsu clan, a settlement was not reached.

After learning that Sagae Kanehiro had approached Yoshiaki again, Terumune became upset and, on 7/25, deployed to Shinjuku in the Yashiro manor.  On 8/4 of Tenshō 2 (1574), Terumune and Yoshiaki engaged in battle at Narage.  On 8/27, Shiratori Nagahisa proposed a settlement.  From 9/1 to 9/9, the Ujiie clan (on behalf of the Mogami) and the Watari clan (on behalf of the Date) conducted negotiations and, on 9/10, a settlement was reached.

Aftermath

The Mogami clan became completely independent of the Date and the alignment of the kokujin, or provincial landowners, of the Mogami and Murayama districts became clear.  The Tendō clan, along with the kunishū in Higashine and Nishine, reconciled with Yoshiaki.  The Shiratori clan, however, could not accept the conditions of settlement.  From 1577, those who had supported Mogami Yoshimori and the Date clan during the conflict, including the kokujin comprising the Eight Shields of the Mogami, along with the Kaminoyama, the Shiratori, the Sagae, and the Daihōji clans, continued to be attacked by Yoshiaki and were destroyed.  The Date clan settled with the Nihonmatsu clan while fighting against the Sōma, actively operating in the southern portion of Mutsu (the Igu District) that was earlier lost during the Tenbun Conflict that ran from 1542 to 1548.