Sekigahara: How Tokugawa Won Japan in a Single Afternoon

The decisive battle of Japanese feudal history lasted, by most accounts, less than six hours. Two coalitions of roughly equal size — the Eastern Army of Tokugawa Ieyasu and the Western Army nominally led by Ishida Mitsunari — collided on October 21st, 1600 at Sekigahara, a narrow basin where three roads converged in Mino Province. By the time the fog lifted in late morning the issue was already being decided not by tactics but by treason.

The Strategic Setup

When Toyotomi Hideyoshi died in 1598 he left a five-year-old heir, Hideyori, and a council of five regents headed by Ieyasu. Within two years the council had broken into two factions: the eastern lords who looked to Ieyasu, and the western lords whom Ishida Mitsunari rallied to defend the Toyotomi succession. By autumn 1600 both sides were marching west along the Tōkaidō. The clash was inevitable; the only question was where.

The Battle

The Western Army arrived first and held the higher ground on three sides of the basin. On paper the position was strong. In reality the coalition was riddled with secret correspondence: Ieyasu had spent the preceding months bribing or threatening at least four major Western commanders into agreeing to switch sides. The most important of these was Kobayakawa Hideaki, holding 15,000 men on Mount Matsuo on the southern flank. When the battle opened in dense fog around eight in the morning, the Eastern center attacked and the Western center held. For four hours the lines barely moved.

Just after noon Ieyasu ordered his arquebusiers to fire on Kobayakawa's stationary troops — a deliberate provocation to force a decision. Kobayakawa, hesitating no longer, charged downhill not against Ieyasu but against his own ally Ōtani Yoshitsugu. Three other Western commanders defected within minutes. The Western line collapsed sideways. By four in the afternoon Mitsunari was fleeing on foot through the hills.

What It Decided

Ieyasu spent the next three years redistributing the realm: more than ninety daimyō houses lost some or all of their lands, and the whole shape of Edo-period Japan — the tozama vs. fudai split, the strategic placement of Tokugawa allies along major roads, the marginalization of the Toyotomi to a single Osaka castle — was set within months of the battle. In 1603 Ieyasu took the title of shogun. The new political geography would last until 1868.

Sekigahara is sometimes called the battle that 'made' the Tokugawa, but it would be more accurate to say it ratified what Ieyasu had already engineered. The fight on the field was almost a formality: the real campaign had been the months of secret letters before sunrise on October 21st.