In the spring of 1467, Kyoto was the heart of Japan. It was the seat of the emperor, the residence of the shogun, the center of Buddhist learning and aristocratic culture, a city of perhaps 100,000 people living in wooden buildings packed close against each other along the grid of streets that had been laid out in the 8th century on the model of Tang dynasty Chang'an. It was also, in the spring of 1467, being cut in half by two armies.

The war had its roots in a problem that should never have become a war. Shogun 足利義政 (Ashikaga Yoshimasa) — 31 years old in 1467, a man of genuine aesthetic refinement and equally genuine indifference to governance — had reached middle age without a clear heir. In 1464, he named his younger brother 足利義視 (Ashikaga Yoshimi) as his successor. The following year, his wife 日野富子 (Hino Tomiko) gave birth to a son, 足利義尚 (Ashikaga Yoshihisa). The succession question instantly became a contest. 細川勝元 (Hosokawa Katsumoto), the powerful shugo (守護, military governor) of several provinces, backed Yoshimi. 山名宗全 (Yamana Sozen), whose clan controlled even more of western Japan, backed Tomiko's infant son. Each man had the resources of multiple provinces and tens of thousands of soldiers behind him.

A secondary conflict accelerated the collision. Within the 畠山 (Hatakeyama) clan, a separate succession dispute had drawn Hosokawa and Yamana to opposite sides. By early 1467, both the shogunal succession crisis and the Hatakeyama conflict were unresolved, the factions fully armed, and the city fully occupied by soldiers who had no intention of leaving until they had won.

The fighting escalated through the spring of 1467. In March, a Hosokawa mansion was burned — the first outbreak of open violence in the capital itself. In the spring months that followed, a Yamana mansion was attacked. Fire spread from the site. In a city of wooden buildings and narrow streets, fire did not respect military objectives. What soldiers set alight in one block became a conflagration three blocks beyond it, consuming residences, shops, and temples that had nothing to do with the political dispute. 足軽 (ashigaru, foot soldiers) — irregular troops, many of them desperate men with no stake in the outcome beyond what they could loot — ranged beyond any formation and burned what they could not carry.

足利義政 (Ashikaga Yoshimasa) watched all of this with what contemporary observers described as a kind of aesthetic detachment. He attended poetry gatherings. He refined his plans for a retirement villa in the eastern hills — the structure that would become 銀閣寺 (Ginkaku-ji, the Silver Pavilion). He issued occasional decrees calling for calm. He did not act. The war that bore the era name of his reign — 応仁 (Onin) — was, to the man in whose name it was being fought, more an inconvenience than a crisis demanding leadership.

By July 1467, Yoshimasa had appointed Hosokawa Katsumoto as commanding general of the Eastern Army — a decision that transformed what had been factional street fighting into something with the formal structure of a civil war. Yamana received massive reinforcements in September: 20,000 troops under 大内政弘 (Ouchi Masahiro) from western Japan. By November, the great Zen temple 相国寺 (Shokoku-ji) had been destroyed — not by deliberate assault, but by fire spreading from nearby combat. Temple fires in 1467 Kyoto were not extraordinary. They were routine.

The scale of the forces involved was staggering for an urban environment. The Eastern Army (Hosokawa) is estimated to have fielded approximately 160,000 troops at its peak; the Western Army (Yamana) approximately 116,000. These figures, drawn from secondary sources, should be treated as approximations — original documents are unreliable on troop counts — but even if the actual numbers were a fraction of these, the effect of armies of that size operating within a city of wooden buildings was catastrophic and foreseeable.

Both 細川勝元 (Hosokawa Katsumoto) and 山名宗全 (Yamana Sozen) died in 1473, within months of each other, their personal rivalry ending in the same year but resolving nothing. The war continued for four more years after its principal leaders were gone, now completely unmoored from its original causes. Historians note that by the mid-1470s, combatants on both sides would have struggled to articulate precisely what they were fighting for. The war ended in 1477 not in victory but in exhaustion.

By then, two-thirds of Kyoto had been destroyed. The population had fled. The aristocracy — the court nobles and their retainers who had given the city its cultural heart — had scattered to the provinces. The 足利幕府 (Ashikaga Shogunate) retained its nominal existence but no longer commanded the authority or resources to impose order on the country. The age of the great 守護大名 (shugo daimyo, military governors) was over. The age of the 戦国大名 (sengoku daimyo, warring states lords) — men who held their domains by force and kept them by force — had begun.

足利義政 (Ashikaga Yoshimasa) outlived the war. He retired to his beloved 銀閣寺 (Ginkaku-ji) in the eastern hills of Kyoto, wrote poetry about moonlight, and died in 1490. The Silver Pavilion was never actually covered in silver. The war he had set in motion — and failed to stop — had created the world that the next century of Japanese history would be spent trying to put back together.