He was not going to fight the Uesugi. He probably never intended to.

On July 24, 1600, 徳川家康 (Tokugawa Ieyasu) departed 大坂城 (Ōsaka-jō — Osaka Castle) at the head of a massive army, bound northeast toward 会津 (Aizu) and a punitive campaign against 上杉景勝 (Uesugi Kagekatsu). The stated casus belli was compelling: Kagekatsu had refused Ieyasu's summons to Osaka, was conducting an alarming military buildup in the northeast, and his chief advisor 直江兼続 (Naoe Kanetsugu) had reportedly replied to Ieyasu's demands with the 直江状 (Naoe-jō) — a letter so contemptuous that it publicly questioned Ieyasu's integrity and honor. The letter, if it said what accounts claim, was an extraordinary provocation addressed to the most powerful man in Japan. (Historians note that only copies of the letter survive; the original has never been found, and some scholars believe it was embellished or partially fabricated after the fact. The "insult" that launched the campaign leading to Sekigahara may have been, at least in part, manufactured.)

Real or amplified, the provocation served its purpose. On July 12, Ieyasu convened a war council at Osaka and required every attending daimyo to pledge support for the campaign against the Uesugi. This was a masterstroke: before Ishida Mitsunari had made a single move, Ieyasu had forced every lord in the room to declare a side. Those who pledged were the Eastern Army. Those who stayed silent or refused would have to show their hand when Mitsunari moved.

Because Mitsunari was going to move. Ieyasu understood this. He could not challenge Mitsunari and the Toyotomi loyalists directly while surrounded by them in Osaka. But an army marching east — absent from the capital, apparently engaged with a distant enemy in the mountains of the northeast — was the opening Mitsunari had been waiting for. By marching east, Ieyasu was not fleeing the threat. He was creating the conditions that would bring it into the open.

The night of July 25, the army stopped at 伏見城 (Fushimi-jō — Fushimi Castle), south of Kyoto. There, Ieyasu spent the evening with 鳥居元忠 (Torii Mototada), his old retainer and friend — a man who had served him for decades, since the dark years when Ieyasu was a hostage in another lord's castle. Mototada was sixty-one years old. He would hold Fushimi Castle against whatever army Mitsunari sent, with approximately 1,800 men. Against forty thousand, as it turned out.

Both men understood the arithmetic. Mototada had asked for this assignment — had reportedly insisted that one of them had to stay behind, that Fushimi Castle was too strategically important to abandon, that this was his role and he was ready for it. Historical accounts record that their parting was not strategic calculation but genuine grief — two old men saying goodbye at a castle gate, one riding east toward the future and one staying behind to buy it.

Ieyasu rode east. The army continued toward Aizu. On September 1, while still on the road, Ieyasu received word that Ishida Mitsunari had raised the Western Army. The trap had sprung — or the gamble had paid, depending on how one reads Ieyasu's intentions. He reversed the entire army and turned west.

Fushimi Castle fell on September 8, after twelve days. The garrison of 1,800 held against Mitsunari's force of 40,000 until fewer than ten defenders remained. 鳥居元忠 (Torii Mototada) committed ritual suicide on September 8, 1600. The blood of his defenders stained the floorboards of the castle's corridors so deeply that, when the castle was later demolished and its wood repurposed, those blood-stained boards were installed as ceiling planks in temples and shrines across Kyoto — walking over such boards was considered disrespectful, so they were placed overhead, as a permanent memorial. Some of those ceilings survive today.

The 関ヶ原の戦い (Sekigahara no Tatakai — Battle of Sekigahara) came on October 21, 1600. Ieyasu won. In 1603 he became Shogun, founding the Tokugawa shogunate that would rule Japan for 268 years.

策略 (Sakuryaku) — strategy, scheme, cunning — is the word for what Ieyasu did on July 24, 1600. Not bravery, not rage, not honor in the traditional sense: a plan that required his friend to die for it to work, constructed with enough care that the friend agreed to play his part willingly. It was perhaps the most consequential march in samurai history. And it was never really about the Uesugi at all.