Battle of Sekigahara (1600): The Battle That Decided Japan

The Battle of Sekigahara was fought on 21 October 1600 in a narrow valley in central Japan between the Eastern Army of Tokugawa Ieyasu and the Western Army of lords loyal to the Toyotomi family, organised by Ishida Mitsunari. Decided by mass defections in the middle of the fighting, it gave Ieyasu control of the country. Within three years he had founded the Tokugawa shogunate, which ruled Japan until 1868.

Background: a power vacuum

When Toyotomi Hideyoshi died in September 1598, his heir Hideyori was only five years old. Hideyoshi had arranged for the country to be governed in Hideyori’s name by a Council of Five Elders, the greatest lords of Japan, and five commissioners (bugyō) responsible for administration.

The most powerful of the elders was Tokugawa Ieyasu, who held the rich Kantō region around Edo, granted to him after the Siege of Odawara in 1590. His main counterweight, the respected elder Maeda Toshiie, died in 1599. Ieyasu then began to act as the real ruler, arranging marriages between his family and other lords without permission and taking up residence in Osaka Castle.

Japan’s lords were also deeply divided by the Imjin War in Korea. Many of the generals who had fought there, such as Katō Kiyomasa and Fukushima Masanori, blamed the commissioner Ishida Mitsunari for unfair reports to Hideyoshi. In 1599 a group of them tried to attack Mitsunari, who was forced into retirement at his castle of Sawayama.

The road to war

In the summer of 1600 Ieyasu led an army north-east to punish Uesugi Kagekatsu, another elder, whom he accused of preparing for war in Aizu. Mitsunari seized the moment. He formed a coalition, persuaded the elder Mōri Terumoto to become its nominal commander in Osaka Castle, and accused Ieyasu of violating Hideyoshi’s will.

The Western Army besieged Fushimi Castle near Kyoto, held by Ieyasu’s old retainer Torii Mototada, who fought to the death; the castle fell on 8 September after a siege of less than two weeks. Ieyasu, meanwhile, met his allied lords at Oyama, where most of them, including former Toyotomi generals who hated Mitsunari, agreed to turn west against him.

The war quickly spread across the country. In Osaka the Western leaders tried to take the families of Eastern lords as hostages; Hosokawa Gracia, the Christian wife of Hosokawa Tadaoki, died rather than be taken, and the plan was largely abandoned. In Kyushu the retired lord Kuroda Yoshitaka (Josui) raised an army and seized Western castles, while in the north Date Masamune and Mogami Yoshiaki fought the Uesugi.

The Eastern Army advanced along the Tōkaidō road and captured Gifu Castle in late September. Ieyasu’s son Tokugawa Hidetada, leading a second army of about 38,000 men along the inland Nakasendō, was held up besieging Sanada Masayuki at Ueda Castle and arrived too late for the battle.

The armies

Both armies are usually estimated at roughly 75,000 to 100,000 men each, though figures vary widely between sources. The Western Army included Ishida Mitsunari, Ukita Hideie, Ōtani Yoshitsugu, Konishi Yukinaga and Shimazu Yoshihiro, as well as the large Mōri contingent and Kobayakawa Hideaki, Hideyoshi’s nephew by marriage.

On paper the Western Army held a strong position. On the night before the battle it took up positions on the hills around the Sekigahara valley, a crossroads where the Nakasendō met roads to the north and west. Kobayakawa’s 15,000 men held Mount Matsuo to the south, and the Mōri forces were on Mount Nangū, behind the Eastern Army’s line of advance.

The weakness was loyalty. Ieyasu had spent months corresponding with Western commanders. Kobayakawa Hideaki had secretly promised to change sides, and Kikkawa Hiroie, a Mōri commander, had agreed that the Mōri troops would not fight.

The battle

The morning of 21 October was foggy. Fighting began at about 8 a.m., when Ii Naomasa and Ieyasu’s son Matsudaira Tadayoshi pushed forward against the Western centre, and Fukushima Masanori’s troops engaged those of Ukita Hideie. For several hours the battle was fierce and evenly balanced; Ishida’s, Ukita’s and Ōtani’s men held their ground.

Mitsunari signalled for Kobayakawa and the Mōri to attack, but they did not move. Kikkawa Hiroie’s troops, placed in front of the main Mōri force under Mōri Hidemoto, blocked the way and stayed still, and Chōsokabe Morichika and others behind them also stood idle.

Around midday Kobayakawa Hideaki finally came down from Mount Matsuo and attacked Ōtani Yoshitsugu’s flank. Tradition says he moved only after Ieyasu ordered his arquebusiers to fire toward Kobayakawa’s position, though some recent historians doubt this story and argue that he defected at the start of the fighting. Ōtani had anticipated treachery and at first threw back the attack, but four other Western commanders, including Wakisaka Yasuharu, then also changed sides.

Ōtani’s force was destroyed and he took his own life. The Western Army collapsed: Konishi and Ukita fled, and Ishida Mitsunari escaped into the mountains. By about 2 p.m. the battle was over.

The Satsuma contingent of Shimazu Yoshihiro, who had refused to take part in the main fighting, found itself surrounded. Rather than flee to the rear, the Shimazu charged forward straight through the Eastern lines. They lost most of their men, including Yoshihiro’s nephew Shimazu Toyohisa, but wounded the Tokugawa commander Ii Naomasa and brought Yoshihiro home to Kyushu. The breakout became one of the most famous episodes of the battle.

Key people

• Tokugawa Ieyasu (1543–1616): commander of the Eastern Army, later the first Tokugawa shogun.
• Ishida Mitsunari (1560–1600): Toyotomi administrator who organised the Western coalition; executed after the battle.
• Kobayakawa Hideaki (1582–1602): Western commander whose defection decided the battle; he died two years later.
• Ōtani Yoshitsugu (born 1558 or 1565, died 1600): Mitsunari’s loyal friend, killed in the battle.
• Shimazu Yoshihiro (1535–1619): Satsuma lord famous for his breakout through enemy lines.

Consequences

Ishida Mitsunari was captured within days and executed in Kyoto on 6 November 1600, with Konishi Yukinaga and the monk Ankokuji Ekei. Ieyasu then redrew the map of Japan. Dozens of Western lords lost their domains entirely, and others, such as the Mōri and Uesugi, had their lands greatly reduced; the Mōri were cut back to Chōshū in the far west. Ieyasu gave the confiscated lands to his own family, his hereditary vassals and the lords who had supported him.

Not every Western lord was punished equally. The Shimazu of Satsuma, far away in southern Kyushu and still strong after their escape, negotiated for two years and in the end kept their entire domain. The Mōri were saved from complete destruction only because Kikkawa Hiroie had kept their troops out of the battle, a bargain that left lasting resentment within the clan.

The distinction between fudai lords, hereditary vassals of the Tokugawa, and tozama or “outside” lords, who had submitted only around 1600, shaped politics for the next two and a half centuries. Ieyasu was appointed shogun by the emperor in 1603, founding the Tokugawa shogunate.

Hideyori and the Toyotomi family remained in Osaka Castle with considerable wealth and prestige. Ieyasu finally destroyed them in the Siege of Osaka in 1614–1615, after which no lord challenged Tokugawa rule for over two centuries.

The battlefield today

Sekigahara remains a small town on the main routes between Kyoto and eastern Japan; the modern railway and expressway follow the same corridor as the old Nakasendō. Stone markers show where the commanders were positioned, including Ieyasu’s final command post and Ishida Mitsunari’s camp on Sasaoyama hill, and two burial mounds for the heads of the dead are preserved. The Gifu Sekigahara Battlefield Memorial Museum, opened in 2020, explains the campaign with maps and displays of armour and weapons.

Myths and facts

Sekigahara is often described as one battle that settled everything in a single day. In reality it was the climax of a nationwide war fought from Kyushu to the far north, including sieges at Fushimi, Ōtsu and Tanabe and fighting between Date Masamune and the Uesugi. Its outcome also depended on months of letters and secret bargains before the armies met.

The story that Kobayakawa Hideaki hesitated until Ieyasu’s guns fired at him is a famous part of the legend, but it rests on later accounts and is questioned by some historians. Casualty figures are also uncertain: estimates of the dead range from several thousand to more than 30,000.

There is a widespread belief that the losers of Sekigahara never forgot their defeat. It is true that the tozama domains of Chōshū and Satsuma led the overthrow of the shogunate in the 1860s, but historians caution against seeing a direct grudge running through 260 years of history.

Timeline

• 1598, 18 September: Toyotomi Hideyoshi dies.
• 1599, April: Maeda Toshiie dies; Ishida Mitsunari is forced into retirement.
• 1600, summer: Ieyasu marches against Uesugi Kagekatsu in Aizu.
• 1600, early September: The Western Army takes Fushimi Castle.
• 1600, late September: The Eastern Army captures Gifu Castle.
• 1600, 21 October: Battle of Sekigahara.
• 1600, 6 November: Ishida Mitsunari is executed in Kyoto.
• 1603, March: Ieyasu is appointed shogun.

Why it matters

Sekigahara ended the long struggle for power that followed Hideyoshi’s death and made Tokugawa Ieyasu the unchallenged ruler of Japan. The settlement that followed created the political order of the Edo period, a long era of peace, isolation and economic growth, and the name Sekigahara is still used in Japanese to mean any decisive showdown.