The Onin War (応仁の乱 Ōnin no ran) was a civil war from 1467 to 1477 during the Muromachi period in Japan. A dispute between Hosokawa Katsumoto and Yamana Souzen escalated into a nationwide war involving the Ashikaga shogunate and various daimyo.

The war initiated the Sengoku Period, "the Age of the Country At War". This period was a long, drawn-out struggle for domination by individual daimyo, resulting in a mass power-struggle between the various houses to dominate the whole of Japan. It was during this time though, that there would emerge three individuals who would later be considered the three great heroes of the Sengoku Period, and who would eventually unite Japan under one house; they were Oda Nobunaga, Toyotomi Hideyoshi, and Tokugawa Ieyasu.

The Onin War began when Shogun Ashikaga Yoshimasa proclaimed his brother, Yoshimi, heir to the shogunate. Yoshimasa even dragged his brother out of a monastery to fulfill his proclamation. A year later, upon the birth of his son Yoshihisa, Yoshimasa changed his mind and decided his son was a better candidate. At the same time though, the Yamana and Hosokawa clans had spent years as rivals, interfering in the affairs of other families and clans with varying degrees of success. With two potential candidates to be the next shogun, it was a given that each family would choose either Yoshihisa or Yoshimasa as who should be the next shogun. Yamana Souzen, referred to as the "Red Monk" - thanks to his horrendous temper and his membership of the priesthood - decided to support the infant heir, Yoshihisa. Hosokawa Katsumoto on the other hand, threw his clan behind Yoshimi, the current shogun’s brother. To make things worse, Yamana Souzen and Hosokawa Katsumoto were related - Souzen was Katsumoto's father-in-law!

After mustering their armies, Yamana - with 80,000 samurai and mercenaries, and Hosokawa - with 85,000 men, met in Kyoto. At this time in history, these numbers were unbelievable, seeing how most European forces numbered only in the low tens of thousands. Neither side though, would risk starting the battle, for fear they would be considered a rebel in the eyes of the Shogun, thus inevitably losing them support throughout Japan. The war did start though, after Yamana pulled in another 20,000 men, and when 'mysteriously,' the Hosokawa mansion burnt to the ground. This act placed the unwanted title of "rebel" upon the Yamana Clan.

By July of 1467 the fighting had become serious, and this when the Onin War officially started. By September, Kyoto's northern parts were in ruin, and everyone who could flee from Kyoto, did.

Both Yamana Souzen and Hosokawa Katsumoto died in 1473, and even then, the war continued on, neither side figuring out how to end the war. However, eventually the Yamana clan lost heart as the label of "rebel" was at last having some effect. Ouchi Masahiro , one of the Yamana generals, eventually burnt down his section of Kyoto and left the area. It was by 1477, some ten years after the fighting had begun, that Kyoto was now nothing more than a place for mobs to loot and move in to take what was left. Neither the Yamana clan, nor the Hosokawa clan had achieved its aims, other than to kill some of the other clan.

During this whole ordeal, the shogun did absolutely nothing. Ashikaga Yoshimasa was only slightly in-tune with reality; and he obviously didn't have a care what was going on in his country. While Kyoto was burning, he spent his time on poetry readings and other cultural activities and in planning the Ginkaku-ji, a Silver Pavilion to rival the Kinkaku-ji, the Golden Pavilion, that his grandfather, Ashikaga Yoshimitsu, had built.

The violence in Kyoto between Yamana and Hosokawa left a bad taste in the mouths of everyone in Japan. The Onin War, and the shogun’s complacent attitude torwards the war, "sanctioned" private wars and skirmishes between the other daimyo. It got to a point where no part of Japan was untouched by violence. The best way to settle any dispute, during this time, appeared to be by the sword. Although the battles in Kyoto had been abandoned, the war had spread over to the rest of Japan. In Yamashiro Province, the Hatakeyama clan had split into two parts that fought each other to a standstill. This stalemate, as well, was to have serious consequences. In 1485, the peasantry and ji-samurai (lesser samurai) just had enough and revolted. Setting up their own army (the 'ikki'), they forced the clan armies to leave the province. The ikki were becoming a powerful force, and not just armed mobs. By 1486 they had even set up a provisional government for Yamashiro province.

The ikki would form and appear throughout the other parts of Japan, such as Kaga Province, where a sect of the Amida Buddhists, the Ikko, started their own revolt during the Onin War after being enlisted by one of Kaga's most prominent warlords, Togashi Masachika . The Ikko were a sect who tried their hardest to appeal to the common peasants in their region, and it was only inevitable that they would form a sort of Ikko-ikki. By 1488 the Ikko-ikki of Kaga Province expelled Masachika and the other warlords, and took control of the province. After this they began building a fortified castle-cathedral along the Yodo River and used it as their Headquarters. The Ikko-ikki and the Yamashiro-ikki were revolutionary, in a process called Gekokujo ("the low oppress the high").

See also

• List of wars
• Military history of Japan