The Battle of Jūgorigahara occurred in the eighth month of Tenshō 16 (1588).  The battle was waged between the allied forces of the Uesugi and Daihōji (the Daihōji-Mutō) on one side and the Mogami army led by Tōzenji Yoshinaga and Tōzenji Katsumasa (siblings) on the other side.

Background

The Shōnai area of Dewa Province was governed by the Daihōji clan (Daihōji-Mutō clan) for generations, but, during the Sengoku period, the clan was beset by a series of internal disputes.  Moreover, by encompassing the Shōnai Plain and Sakata Harbor, this area had significant economic value and was sought by neighboring clans including the Uesugi, the Mogami, and the Onodera.

In the 1580’s, Mogami Yoshiaki, the lord of Yamagata Castle, rapidly expanded his territory so that attacks eventually extended into the Shōnai.  Daihōji Yoshiuji (Mutō Yoshiuji), the lord of Oura Castle, together with help from Honjō Shigenaga (an ally of the Daihōji from the era of Yoshiuji’s father, Daihōji Yoshimasu), resisted the attacks.  In 1583, Yoshiaki leveraged a senior retainer of the Mutō clan named Tōzenji Yoshinaga, the lord of Tōzenji Castle, to assassinate Yoshiuji.  In the eleventh month of 1587, he then attacked Yoshiuji’s successor (his younger brother named Daihōji Yoshioki) and killed him too.  Having garnered control of the Shōnai, Yoshiaki ordered the Tōzenji clan to govern the territory.  At this time, Honjō Shigenaga, the adopted son of Yoshioki, along with his son, Daihōji Yoshikatsu (Honjō Mitsunaga), fled for protection under his natural father, pledging to recoup their strength for a renewed attack.  Thereafter, the Daihōji came fully under the influence of the Uesugi clan.

In the first month of 1588, Date Masamune intervened militarily in an internal dispute within the Ōsaki clan (the original home of his formal wife) under the main branch of the Mogami clan.  This event is known as the Battle of Ōsaki.  In a bid to eliminate Masamune, Yoshiaki dispatched reinforcements to the territory of the Ōsaki and, at the same time, deployed for the conduct of widespread attacks in the territory of the Date.  Taking advantage of Yoshiaki’s preoccupation with fighting against Masamune, Uesugi Kagekatsu moved his forces to occupy the Shōnai.

Course of events

In the eighth month, Kagekatsu (the seventeenth head of the Uesugi family of Echigo Province) ordered his retainers, Honjō Shigenaga and Daihōji Yoshikatsu (father and son), to lead Uesugi forces on attacks in the Shōnai.  After toppling the auxiliary castles of Sekine and Kiyomizu, the Uesugi headed toward Oura Castle.  Tōzenji Yoshinaga and Tōzenji Katsumasa (father and son) decided to intercept them in a field battle, leading to a confrontation on the Jūgori Plain known as Jūgorigahara.  In the initial stages of the battle, the armies were evenly matched, but the inferior number of Mogami forces gradually led to their disadvantage.  First, Yoshinaga plunged forward into the main formation of the enemy and was killed.  Upon hearing this news, Katsumasa followed with another individual assault against the Uesugi army, cutting his way toward an unsuspecting Shigenaga.  With a single blow from Katsumasa, Shigenaga’s helmet was cut from the temple to below the ear, after which Katsumasa was killed by Shigenaga and his close retainers.

After suffering defeat, Nakayama Genba, the chamberlain of Oura Castle, retreated to the Mogami.  The Mogami army continued to resist but, also in 1588, lost at the Siege of Asahiyama Castle while Kagekatsu took control of the Shōani region.  Shigenaga chased remaining forces and advanced further, but withdrew after encountering a fierce counterattack by the Mogami at Higashine.

Yoshikatsu revived the Mutō clan and, through the introduction of Uesugi Kagekatsu, served Toyotomi Hideyoshi.  However, in 1591, he was banished to Yamato Province and his territory given to the Uesugi clan.

Aftermath of the battle

This battle occurred after the issuance of an order by Toyotomi Hideyoshi in the twelfth month of 1587 prohibiting personal battles between daimyō.  Consequently, this deployment would not have been authorized.  Hideyoshi, however, implicitly permitted the recovery of the Shōnai area by Daihōji Yoshikatsu.  On 8/23 of 1590, uprisings occurred in the Fujishima area of Dewa against land surveys in the Shōnai area conducted by the Uesugi which were part of a nationwide order from Hideyoshi.  In 1591, after Yoshikatsu was removed from his position based on suspicion of inciting the uprisings, the Shōnai was allocated to Kagekatsu.  Owing to this verdict along with death of his second daughter, Komahime, in connection with the Hidetsugu Incident, Mogami Yoshiaki held deep suspicion and enmity to Hideyoshi and the Uesugi clan.  This may have been the reason why he allied with Tokugawa Ieyasu at the Battle of Sekigahara.

In 1600, at the Battle of Keichō Dewa, the Mogami attacked and defeated the Uesugi who had sided with the Western Army in connection with the Battle of Sekigahara.  After the battle, in the fourth month of 1601, Yoshiaki reclaimed the Shōnai and assigned Shimoji Uemon Yoshitada to become lord of Oura Castle with a fief of 12,000 koku, securing the Tagawa District.  Oura was renovated with the main structures on the plain below the mountain and renamed Ōyama Castle.  In 1615, a fief of 20,000 koku was awarded to Ōyama Chikuzen-no-kami (the younger brother of Mogami Iechika); however, owing to orders issued by the Edo bakufu in the eleventh month of 1615 permitting one castle per province, the castle was abandoned.  Following removal of the Mogami from their position in 1622, a majority of the Shōnai became the domain of the Sakai clan who, in turn, assigned the former castle to a cadet family and local officials of the Edo bakufu.

Anecdotes

When Masakatsu attacked Shigenaga, he wielded a precious and ancient sword from one of Japan’s most famous swordsmiths named Masamune dating from the late Kamakura period.  After Shigenaga acquired this sword, it was referred to as the Honjō Masamune.  After passing hands through several owners, it was finally presented to Tokugawa Ieyasu, and from the time of Tokugawa Ietsuna (1641 to 1680), became the most precious family heirloom of the shōgun family.  However, during the occupation of Japan after World War II, the last known owner of the Honjō Masamune, Tokugawa Iemasa, a descendant of the shōgun family, obeyed a general order issued by General MacArthur, the Supreme Commander of the Allied Powers, requiring total disarmament and delivered the family swords to the Mejiro police station in Tōkyō, after which the whereabouts of the sword are unknown.

The helmet worn by Honjō Shigenaga during this battle is kept in a museum in the City of Murakami in the northern part of Niigata Prefecture (formerly Echigo Province).  It has a cut from a blade on the right side but not as described according to legend.