The last rival was six weeks in the ground. 豊臣秀頼 (Toyotomi Hideyori) had died on June 4, 1615, in a burning castle in Osaka, twenty-one years old, the final obstacle to absolute Tokugawa dominance erased. Japan was at peace for the first time in living memory. And Ieyasu, age seventy-two, understood with cold clarity what peace meant: warriors with no wars are dangerous animals, and Japan had roughly 400,000 of them.

In approximately early August 1615, the retired shogun convened the major daimyo of Japan at Fushimi Castle — itself a symbol of the Toyotomi world now under Tokugawa control — and had the 武家諸法度 (Buke Shohatto), the Laws for Military Houses, read aloud to them. Thirteen articles. A rulebook for a warrior class in a country that had just run out of wars.

The opening is what surprises. Article 1 does not begin with a prohibition. It begins with an instruction: samurai must pursue both the martial arts and literature — 武 (bu) and 文 (bun) together, the sword and the book held in equal hands. The code that would govern Japan's warriors for 250 years opened by telling them to read. This was not sentimentality. It was architecture. A samurai absorbed in scholarship was a samurai not sharpening his sword and measuring his neighbor's walls.

Then came the mechanism of control. Daimyo could not repair their castles without first reporting to the shogunate. They could not arrange marriages — the most intimate dynastic decisions — without Tokugawa approval. They could not form political alliances, recruit 浪人 (rōnin) in suspicious numbers, or build ships above a certain size. Each restriction sealed off another avenue for rebellion.

But the most elegant provision was Article 7: daimyo were required to report any suspicious military activity by neighboring lords immediately. The samurai class was conscripted into its own surveillance. Every powerful lord became a potential informant on every other. Loyalty to the shogunate and self-interest pointed in the same direction: report your neighbor before your neighbor reports you.

The penalty for violation was 改易 (kaieki) — complete confiscation of one's domain. The Tokugawa had already demonstrated, in the chaos following Sekigahara, that they would apply this punishment without hesitation. The code did not need to be enforced daily because the threat alone reshaped behavior.

Ieyasu died in 1616, one year after issuing the code. But his successor Hidetada reissued and tightened it, as did Iemitsu in 1635 — adding the 参勤交代 (sankin-kōtai) requirement that forced daimyo to spend alternating years in Edo, draining their finances and keeping them perpetually in motion, far from their power bases. The 1615 code was a seed. What grew from it was a surveillance state so thorough, so finely calibrated, that Japan's warriors would not fight each other again for 250 years.