The Battle of Sekigahara (Shinjitai: 関ヶ原の戦い; Kyūjitai: 關ヶ原の戰い, Hepburn romanization: Sekigahara no Tatakai) was an important battle in Japan which occurred on October 21, 1600 (Keichō 5, 15th day of the 9th month) in what is now Gifu Prefecture, Japan, at the end of the Sengoku period.
This battle was fought by the forces of Tokugawa Ieyasu against a coalition loyal to the Toyotomi clan, led by Ishida Mitsunari on behalf of the young child Toyotomi Hideyori, from which several commanders defected before or during the battle, leading to a Tokugawa victory. The Battle of Sekigahara is often regarded as the most important battle in Japanese history.
Mitsunari's defeat in the Battle of Sekigahara is generally considered to be the beginning point of the Tokugawa shogunate, which ruled Japan for two and a half centuries until 1868.
Background
The final years of Toyotomi Hideyoshi's reign were turbulent. At the time of Hideyoshi's death, his heir, Toyotomi Hideyori, was only 5 years old, causing a power vacuum in Japan.
Feuding factions
In the years following the Imjin War and the death of Hideyoshi, factional disputes arose between Ishida Mitsunari and seven former Toyotomi generals including Katō Kiyomasa. After the subsequent death of Maeda Toshiie, a powerful and long-term ally of Hideyoshi and Oda Nobunaga, who had been sympathetic to Mitsunari's posturing, the uneasy balance of power began to dissolve. Tokugawa Ieyasu gathered both Kiyomasa and Fukushima Masanori to his cause in a bid to challenge the opposition from Mitsunari, who claimed to fight on behalf of the Toyotomi clan.
At this time, political tensions were high in the capital. In 1599, when the relationship between Ieyasu and Maeda Toshiie became strained and rumors of an attempted conspiracy to storm the Tokugawa residence spread, Yoshitsugu accompanied Fukushima Masanori and other military commanders of the Toyotomi clan to the Tokugawa residence to guard Ieyasu. Later, when rumors of a plot to assassinate Ieyasu by Maeda Toshinaga emerged, Yoshitsugu led an army to Echizen with the inner circle of Ishida Mitsunari, who had been ousted by Ieyasu. Maeda Toshinaga, who was accused of being involved in such conspiracies and contentiously but peacefully made to marry into the Tokugawa clan. Uesugi Kagekatsu, one of Hideyori's regents, stood against Ieyasu by building up his army, which Ieyasu officially questioned, demanding answers from Kyoto about Kagekatsu's suspicious activity. Naoe Kanetsugu responded with a mocking letter highlighting Ieyasu's own violations of Hideyoshi's orders.
Mitsunari met with Ōtani Yoshitsugu, Mashita Nagamori and Ankokuji Ekei, conspiring to raise an anti-Tokugawa army, of which Mōri Terumoto was appointed to be the overall commander. This coalition formed what came to be referred to as the Western Army. Terumoto immediately marched and captured Osaka Castle while the main army of the Tokugawa were still on their way to suppress Kagekatsu.
At first, Mitsunari wanted to use Gifu Castle, which at that time was commanded by Oda Hidenobu (the grandson of Nobunaga), and Ōgaki Castle as choke points to impede the advances of the Eastern Army (the Tokugawa-led coalition). However, this plan was foiled by a number of campaign events:
Following these failures and the threat against Osaka Castle, Mitsunari changed his plan and prepared his army for an open battle on the field of Sekigahara against the main body of the Eastern Army, led by Ieyasu. As preparation for this inevitable conflict, Ieyasu had purchased massive quantities of Tanegashima matchlocks.
However, one day before the beginning of the battle, Kikkawa Hiroie, vassal of the Western Army-allied Mōri clan, colluded with the Eastern Army and promised that the Mōri clan would change sides during the battle, on the condition they would be pardoned after the war. Kuroda Yoshitaka and Kuroda Nagamasa served as representatives of the Eastern Army in this correspondence with Hiroie. Hiroie and his senior retainer Fukubara Hirotoshi presented hostages to the Tokugawa side as proof for their cooperation with the latter.
Battle
At dawn on October 21, 1600, the Tokugawa advance guard stumbled into Ishida's army; neither side saw each other because of dense fog caused by earlier rains. Both sides panicked and withdrew, but each was now aware of their adversary's presence and location. Mitsunari placed his position in defensive formation, while Ieyasu deployed his forces south of the Western Army position. Last-minute orders were issued and the battle began. Traditional opinion has stated the battle began around 08:00. However, recent Japanese historians' research estimates that the battle actually began closer to 10:00.
The battle started when Ii Naomasa, previously heavily involved in the Battle of Gifu Castle, commanded his famed unit of 3,600 crimson-clad Ii no Akazonae ("Ii's red devils") to attack the center of the Western Army. According to historian Watanabe Daimon, by many indications of the battle records, the assignment of Naomasa as ichiban-yari (the first unit to engage the enemy) suggests the armies may have already been settled before the battle. Fukushima Masanori concurred with Naomasa's intention to lead the first attack, as Naomasa was appointed by Ieyasu as the supreme field commander and was therefore responsible for all commands and strategies during the battle.
Naomasa charged forward with 30 spearmen and clashed with the ranks of the Western Army. Meanwhile, Fukushima Masanori advanced from his position, following Naomasa and immediately engaging with troops led by Ukita Hideie.
At this point, the battle entered a deadlock. Ōta Gyūichi, who was present at the battle, wrote in his chronicle that "friends and foes are pushing each other" and "gunfire thunders while hails of arrows fly in the sky". According to records from Spanish accounts, 19 cannons from the De Liefde, a Dutch trading ship, were also used by the Tokugawa army in this battle as field artillery. Kani Saizō, the forerunner of Fukushima Masanori's army, was recorded for taking the heads of 17 enemy combatants he killed during combat near Gifu Castle, and was noted by Ieyasu himself with praise after the battle concluded
Famous swordsman Yagyū Munenori also reported being participated on the side of Eastern Army, where he was later given 2,000 koku in Yamato Province as recognition for his merit in this battle.
Western Army defectors
During the Battle of Sekigahara, several commanders of the Western Army changed sides, allying with the Tokugawa and changing the course of the battle. Perhaps the most notable of these defectors was Kobayakawa Hideaki, the nephew of Toyotomi Hideyoshi, whose disgruntlement with his uncle was exploited by the Tokugawa to sway his loyalty. Two prevailing theories exist regarding the timeline of Hideaki's defection:
- The conventional theory regarding Hideaki's betrayal suggests that the defection occurred partway through the battle. Although he had agreed to defect to the Tokugawa side beforehand, Hideaki was allegedly hesitant during the battle and remained neutral, reportedly only joining the battle around noon as a member of the Eastern Army. Some later historical accounts claim that as the battle grew more intense, Ieyasu finally ordered his arquebuses to fire at Kobayakawa's position on Mt. Matsuo to force a choice. This version allegedly originated from an anecdote about Hideaki dating to the Edo period.
- Modern Japanese researchers of Sekigahara, such as Jun Shiramine and Junji Mitsunari, have advanced the theory that Hideaki had already defected to the side of Tokugawa by the start of the battle, based on correspondence documents between Hideaki and Kuroda Nagamasa before the battle, as well as Ōtani Yoshitsugu's army position at the start of the battle suggesting foreknowledge by the Western Army of Hideaki's betrayal. Historian Stephen Turnbull also argues that the sheer distance between the Eastern Army positions and that of Kobayakawa, far out of range of arquebuses and likely too far for a shot to even be heard, makes the "story about Ieyasu ordering ‘cannon-shot’ into his ranks" to force Hideaki's hand very unlikely. Furthermore, Masayuki Fujimoto argues the notion of Ieyasu' shooting cannot be corroborated by reliable historical sources of that time. Similarly, another historian, Yūichi Goza explains that the story of Ieyasu shooting at Hideaki's location comes from secondary sources from the Edo period, suggesting it may have been the result of dramatization and embellishment from pro-Tokugawa shogunate historiography to aggrandize Ieyasu's success in Sekigahara. In fact, Goza explained that according to the theory of Jun Shiramine and other Japanese historian Takahashi Yōsuke, the reason why Mitsunari moved from Ogaki Castle to Sekigahara was not because they were enticed to confront the Eastern Army there, but because Mitsunari had learned Hideaki's betrayal even before the battle, and he wanted to rescue Otani Yoshitsugu, who was already arrived at Sekigahara.
Regardless of what actually transpired, the turncoat Kobayakawa forces overwhelmed Yoshitsugu's position, as according to Nakatomi Yūhan-ki (臣祐範記), "The armies of Kamigata (referring to Western Army) had the upper hand, until Kobayakawa Hideaki betrayed them and attacked them from behind with over 15,000 men." At the same time, Yoshitsugu's troops also engaged the units led by Tōdō Takatora, while subsequently Oda Nagamasu and Honda Tadakatsu moved forward and intercepted the Toda Katsunari units attacking Masanori's flank. This intercepting movement resulted in Katsunari's death in combat.
Following the defection of Hideaki, Western Army leaders Wakisaka Yasuharu, Ogawa Suketada, Akaza Naoyasu and Kutsuki Mototsuna also changed sides, further turning the battle in the Eastern Army's favor. These four commanders are recorded to have established contact and concluded deals with Tōdō Takatora, one of the main commanders of the Eastern Army, several days before the battle.
Mōri Terumoto, then daimyō of the Mōri clan, also defected from the Western Army during the battle by keeping his forces entrenched at Osaka Castle rather than joining the battle, then sending his vassal Kikkawa Hiroie to quietly surrender to Ieyasu afterward. Professor Yoshiji Yamasaki of Toho University states that any neutrality-for-territorial-preservation agreement was ineffective at best and badly backfired for the Mōri at worst, as their domains were greatly reduced by the Tokugawa following the battle, and some Mōri troops notably did fight with the Western Army at Sekigahara rather than maintaining their neutrality. Sentiments of defection were divided among the Mōri; Mōri Hidemoto, cousin of and commander under Terumoto, genuinely attempted to meet and aid the Western Army, though his efforts were sabotaged by Hiroie, who, under the pretense of being busy eating his meal, stationed his troops in front of Hidemoto, obstructing them from advancing and relieving Mitsunari. Hiroie also obstructed another Western Army contingent led by daimyō Chōsokabe Morichika from marching and attacking the Tokugawa forces.
Collapse of the Western Army
One of the first and most notable weak points within the Western Army forces developed on Ukita Hideie's front. During the engagement, Hideie's forces began to wane and were steadily overcome by the forces of Fukushima Masanori due to the latter's superior troop quality. The disparity in combat effectiveness may have been attributable to the prior insurrection within the Ukita clan, which caused many senior samurai vassals of the Ukita to desert and join the Tokugawa faction. Hideie was thereby forced to enter Sekigahara with fresh recruits of rōnin mercenaries to fill the gap left within his army. This proved fatal over the course of long-term combat against the Fukushima clan's more disciplined and trained regular troops; the Ukita clan ranks began to break and finally collapse under pressure despite outnumbering the Fukushima.