21 October 1600

A Japanese print of the Tokugawa clan leader, Ieyasu, whose victory over rival clans at the Battle of Sekigahara in October 1600 ended Japan’s civil wars and initiated the 250-year period of the Tokugawa shogunate. During the battle the 16,000 men of Kobayakawa Hideaki changed sides to support Ieyasu, sealing his victory.

There are few battles in Japanese history more famous than the clash between the so-called Western and Eastern armies in a brief civil war to decide who would become the new military hegemon of Japan. The country’s imperial system was dominated by the military leaders, who jockeyed for influence over the imperial court. At Sekigahara on the island of Honshu, the great regional lords, or daimyo, clashed over the rival claims of the Tokugawa and Toyotomi clans to dominate Japan. The battlefield was as much a political as a military site. A number of daimyo fighting for the Toyotomi Western Army hedged their bets about the outcome, uncertain whether to switch loyalty to the enemy commander, Tokugawa Ieyasu. At the last moment, with the outcome in the balance, Kobayakawa Hideaki, son of one of the guardians of the young Toyotomi heir, switched sides and victory went to the Eastern Army, opening the way to the long and relatively peaceful Tokugawa era.

Japanese politics in the late sixteenth century was dominated by the Toyotomi clan and its leader, Hideyoshi, who by the 1590s had imposed a fragile political unity on the whole of Japan. Failure in war in Korea weakened the Toyotomi hold over the rival daimyo. That hold was further weakened when Hideyoshi died in 1599, leaving a five-year-old son, Toyotomi Hideyori, as his successor. Before his death, Hideyoshi established a board of five regents (tairo) to rule on his son’s behalf and five administrators (bugyo) to oversee the running of the state. Within two years the two groups split into rival factions. While Hideyori and his mother sheltered in the powerful castle at Osaka, Tokugawa Ieyasu, the most senior military commander and a powerful landowner, built an alliance to support his efforts to supplant the Toyotomi. The daimyo still loyal to the Toyotomi succession, their land based chiefly in the west of the Japanese islands, gathered around the figure of Ishida Mitsunari, one of the leading bugyo. They also made their base at Osaka Castle, where the infant Hideyori was protected by the daimyo Mori Hidemoto, one of those who was to play a double game at Sekigahara.

The clash between the two sides gathered pace in the summer and autumn of 1600 as each side sought to win over the allegiance of daimyo who hesitated to commit themselves. The Western Army captured the Tokugawa fortress of Fushimi while Tokugawa Ieyasu gathered a force of 30,000 of his own followers and 40,000 from his allies and marched towards Osaka. Ishida’s army numbered an estimated 80,000, but the reliability of many of his allies, already secretly in contact with Ieyasu, was doubtful. After a difficult march through heavy rain, the Western Army arrived at Sekigahara, where Ishida deployed his troops on hilly ground, protected on either flank by a stream, to await the oncoming Eastern Army. On 20 October 1600 (the Japanese fourteenth day of the ninth month), Ieyasu learned that the enemy was waiting for him at Sekigahara and the following morning, in heavy fog, the two armies stumbled into each other. As the fog lifted, the two armies stood face-to-face, an array of heavily armoured samurai armed with their traditional swords and bows, some on horseback. They were backed by a militia of light infantry carrying the traditional spear (naginata). Both sides had cannon, though Ishida’s artillery was hamstrung by the rain, which had soaked the gunpowder. Ieyasu had brought a supply of arquebuses to add to the traditional weaponry of the Japanese soldiers. He placed his allies in the front line, his own retainers in the reserve. At mid-morning, his ally Fukushima Masanori began the battle by launching his advance guard along the River Fuji against the right wing of the Western Army.

The details of the battle are sparse. Ieyasu followed Fukushima’s assault across the rain-soaked ground against the Western left. The samurai, like European knights, were the fighting elite, trained from a young age for mortal combat. ‘The way of the samurai,’ wrote one sixteenth-century soldier, ‘is desperateness. Ten men or more cannot kill such a man.’ As both assaults pushed forward, Fukushima’s flank lay open to attack. Otani Yoshitsugu, a former ‘chief-of-staff’ of the Toyotomi army in Korea, crossed Mount Fuji to attack Fukushima’s forces, who were already engaged in a fierce contest. At this point, Otani should have been supported by the 16,000 men of Kobayakawa Hideaki, stationed behind him on Mount Matsuo. Ieyasu ordered the arquebuses to open fire on the hill and as he did so, the young Hideaki, smarting from Ishida’s accusation of incompetence and encouraged to defect by a Christian daimyo, Dom Daimia Kuroda, decided that his allegiance to the Western Army was no longer useful. He charged into the fray against Otani and turned the tide of the battle. Seeing Hideaki’s disloyalty, and fearing its consequences, four other commanders switched sides. Behind the Western Army stood the reserve of Mori Hidemoto, with 15,000 soldiers. He, too, doomed Ishida by remaining largely inactive. The political calculations on the battlefield made the difference between defeat and victory, for the Western Army was not only larger, but had more battle experience from the war in Korea. This army now disintegrated and fled. Ishida and two of his leading commanders, Konishi Yukinaga and Ankokuji Ekei, were captured and later publicly executed. The casualties suffered by both sides in a long and bitter battle are unknown.

The victory at Sekigahara confirmed Tokugawa Ieyasu as the military hegemon in Japan, though the defeated Western clans acknowledged his claim with reluctance. In 1603, the emperor Go-Yozei installed Ieyasu as sei-i tai-shogun, chief of the Japanese warrior estate and in effect the dominant political authority in Japan. Ieyasu took land away from the defeated daimyo of the Western Army and re-distributed it to his allies and those who had switched sides so auspiciously during the battle. The Christian daimyo, Kuroda, who played a key role in persuading Hideaki to change sides, was presented with a large fiefdom. In 1605, Ieyasu made his son Hidetada shogun in his place, initiating what was to be a 250-year dynasty of the Tokugawa.