[1598–1603] Rise of Tokugawa and the Battle of Sekigahara

The year is 1598. Within the ornate, sprawling complexes of Fushimi Castle, the undisputed ruler of Japan, Toyotomi Hideyoshi, is dying. A man who rose from a peasant’s son to the pinnacle of power, the Taiko, or retired regent, had achieved what generations before him could not: the unification of Japan after a century of ceaseless civil war. But his legacy was fragile, resting entirely on the shoulders of his five-year-old son, Hideyori. As his life faded, Hideyoshi’s final act was one of desperate political engineering. He created a Council of Five Elders, a board of the most powerful daimyo, or feudal lords, in the land. He made them swear a hundred oaths, signing in their own blood, to protect his son and govern until he came of age. At the head of this council, first among equals, sat the patient, calculating, and immensely powerful Tokugawa Ieyasu.

Ieyasu, lord of the vast Kanto plain and master of the newly established castle town of Edo, what we now call Tokyo, was a man forged in conflict. He had waited his entire life for this moment. While the other lords saw a regency, Ieyasu saw a power vacuum. Hideyoshi’s ink was barely dry on the oaths when Ieyasu began to systematically dismantle them. He arranged political marriages for his children, forging alliances with other powerful daimyo clans—a direct violation of Hideyoshi’s decrees. He acted not as a regent, but as a ruler in his own right. This did not go unnoticed. The opposition found its champion in Ishida Mitsunari, a brilliant but famously abrasive administrator who was fiercely loyal to the memory of Hideyoshi and the future of his son. Mitsunari was no great warrior, but he was a master of logistics and politics. He saw Ieyasu’s ambition for what it was: a threat to the Toyotomi clan and the stability of the realm.

The simmering tension boiled over in the year 1600. Japan began to split into two massive factions. The ‘Eastern Army’ coalesced around Tokugawa Ieyasu, a coalition of powerful lords from the east who were either allied to him by marriage, indebted to him for past favors, or simply saw him as the strongest horse to bet on. Against them stood the ‘Western Army,’ a collection of lords loyal to the Toyotomi legacy, marshaled by the tireless Ishida Mitsunari from the strategic stronghold of Osaka Castle, where the young heir Hideyori resided. The air across the archipelago grew thick with the metallic scent of war. Samurai across hundreds of domains began polishing their lacquered armor, sharpening their katana, and checking the mechanisms of their tanegashima arquebuses—the matchlock firearms that had revolutionized Japanese warfare since their introduction by the Portuguese fifty years prior.

Ieyasu, a master of deception, created a pretext. He announced he was leading his army north to subdue a defiant clan, deliberately drawing himself away from the central provinces. It was the move Mitsunari was waiting for. With Ieyasu occupied, Mitsunari officially declared war, hoping to trap him between the northern campaign and the main Western Army. But Ieyasu had anticipated this. He swiftly abandoned his northern campaign, wheeling his massive army around and force-marching them west along the Tokaido road at a punishing pace. The two greatest armies Japan had ever seen were now on a collision course, destined to meet in a narrow valley in central Japan, a place whose name would become synonymous with the birth of an era: Sekigahara.

On the cold, damp morning of October 21, 1600, a thick fog blanketed the Sekigahara valley. The conditions were miserable, the ground a muddy quagmire from recent rains. The Western Army, numbering around 80,000 samurai, held the high ground and a superior tactical position, encircling Ieyasu’s landing points. Ishida Mitsunari had positioned his command post with a clear view of the battlefield, confident in his numbers and his position. Below, the 74,000 men of the Eastern Army, led personally by Tokugawa Ieyasu, were trapped. As the fog began to lift around 8 a.m., the battle began not with a formal charge, but with a chaotic, violent explosion of action. The roar of thousands of matchlock guns echoed like thunder through the valley, followed by the terrifying, rhythmic shouts of samurai charging into the fray, their colorful banners, or sashimono, flapping wildly on their backs.

For hours, the battle was a brutal stalemate. The Western forces pressed their advantage, pushing Ieyasu’s men back. The fighting was ferocious, a desperate clash of yari spears and razor-sharp swords. Ieyasu, stationed at his command post at the rear, grew increasingly anxious. His victory depended not just on the strength of his own loyal troops, but on the treachery he had cultivated in the weeks leading up to the battle. His gaze repeatedly went to the slopes of Mount Matsuo, where 15,000 samurai under the command of a young daimyo, Kobayakawa Hideaki, sat motionless. Kobayakawa had secretly promised to defect to Ieyasu, but now, as the battle raged, he hesitated. Mitsunari sent frantic signals for him to charge and crush Ieyasu's flank, but the young lord would not move.

By midday, Ieyasu’s patience was gone. His center was beginning to buckle. In a moment of calculated fury, he ordered his own arquebusiers to fire upon Kobayakawa's position on the mountain. It was not an attack meant to destroy, but a message, a violent and unmistakable demand: