関ヶ原の戦い

The Battle of Sekigahara was a decisive battle on September 15, 1600 (on the ancient Chinese calendar, October 21 on the modern calendar) that cleared the path to the Shogunate for Tokugawa Ieyasu and his descendants. Though it would take three more years for Ieyasu to consolidate his position of power over the daimyo, Sekigahara is widely considered to be the unofficial beginning of the Tokugawa Bakufu, the final Shogunate to control Japan.

Background
Toyotomi Hideyoshi arranged for a 'council of five' of his most powerful retainers to rule Japan until his son was old enough to rule by himself. His hope was that the five daimyo would effectively balance each other and prevent any one of them from taking control. No such luck. The daimyo quickly prepared for war -- most of them opting to join an anti-Tokugawa coalition. Tokugawa Ieyasu was the strongest of the daimyo. Apparently he did not actively seek to bring his enemies to battle, but when they threw down the gauntlet, he did not mind a chance to fight.

That chance came at Sekigahara in what is now Gifu Prefecture. Although the battle was close, in the end Tokugawa Ieyasu and his allies won a decisive victory.

Wikipedia ~ the free encyclopedia - Battle of Sekigahara