What was the Honnoji Incident?
The Honnoji Incident is the assassination of Oda Nobunaga by his own senior general Akechi Mitsuhide in Kyoto in June 1582. Nobunaga, staying at the temple of Honnoji with a guard of a few dozen men, was surrounded at dawn and died in the burning building. His heir Nobutada was killed the same morning nearby.
It is the single most consequential event of the Sengoku period after Okehazama, and the most argued-about, because no contemporary source records why Mitsuhide did it.
Why did it happen?
Nobunaga had deployed his armies outward on every front: Toyotomi Hideyoshi west against the Mori, Shibata Katsuie north against the Uesugi, others in Shikoku and the Kanto. He himself was in the capital with almost no troops, waiting to move west.
Mitsuhide had been ordered to reinforce Hideyoshi. He had an army of around 13,000 in the field, and he was closer to Kyoto than anyone who could have stopped him.
Forces and sides
Mitsuhide committed roughly 13,000 men. Nobunaga had a personal guard usually described as between twenty and a few hundred, including attendants and pages.
This was not a battle. It was the destruction of an unprotected headquarters.
What happened?
The Akechi army crossed the Katsura river before dawn. The line attributed to Mitsuhide at that moment — "the enemy is at Honnoji" — appears in later accounts and cannot be verified.
Nobunaga's guard resisted briefly. The Shincho Koki records him fighting with a bow until the string broke, then with a spear, and finally withdrawing into the interior of the temple as it burned. His body was never identified in the wreckage, which is one reason rumours about his survival began immediately.
Nobutada, staying separately, attempted to reach his father, then fortified himself at the Nijo residence and was killed there.
Turning point
What decided the following two weeks was not the killing but the reaction to it. Mitsuhide expected support from major houses connected to him and did not get it: his son-in-law Hosokawa Tadaoki refused, and others waited.
Meanwhile Hideyoshi, 200 kilometres away, made peace with the Mori within a day and marched back at a speed nobody anticipated. See Battle of Yamazaki.
Outcome
Mitsuhide held Kyoto for thirteen days before being defeated and killed. The Oda house, deprived of both its head and his heir, fractured into factions that Hideyoshi then defeated one by one.
The unification of Japan continued, but under a different family and with a different character.
Why it mattered
Every theory about Mitsuhide's motive — humiliation, fear of demotion, defence of the imperial court or the shogunate, obligations to the Chosokabe of Shikoku whose destruction Nobunaga had just ordered, a conspiracy involving Hideyoshi or Ieyasu — rests on later testimony, inference, or documents whose interpretation is contested.
The honest position is that the act is certain and the reason is not. Japanese historians have been arguing about it for four centuries and the argument is still live, which is exactly why it remains the most famous unsolved question in Japanese history.
Popular accounts often state a motive with confidence. Contemporary sources — including the diaries of Kyoto nobles and Jesuit correspondence — record the event and the shock, not the reason.
