In the mountains of Gifu Province, roughly 160,000 samurai from rival coalitions clashed in what became the largest and most decisive battle in Japanese feudal history. Tokugawa Ieyasu's eastern army defeated the western coalition loyal to the Toyotomi clan, a victory that ended decades of civil war and established the Tokugawa shogunate, which would govern Japan until 1868.
The battle unfolded in fog and rain across a narrow valley, with roughly 75,000 troops loyal to Tokugawa Ieyasu facing some 85,000 men of the western coalition nominally fighting to preserve power for the young heir of the late ruler Toyotomi Hideyoshi. Ieyasu had spent years quietly building alliances and bribing key commanders, and it paid off spectacularly: the defection of general Kobayakawa Hideaki's 15,000 troops mid-battle broke the western line and turned an even fight into a rout.
By the time the fighting ended that afternoon, an estimated 30,000 men lay dead, and Ieyasu's dominance over Japan was effectively assured, though he did not formally take the title of shogun until 1603.
The Tokugawa shogunate that followed imposed over two centuries of relative peace—the Edo period—built on rigid social hierarchy, isolation from most foreign contact, and the systematic disarmament of rival lords. Sekigahara is remembered in Japan the way Hastings or Gettysburg is remembered elsewhere: the single afternoon that decided the shape of a nation for generations.