The was the assassination of Japanese daimyo Oda Nobunaga at Honnō-ji temple in Kyoto on 21 June 1582 A.D. (2nd day of the sixth month, Tenshō 10). Nobunaga was on the verge of unifying the country, but died in the unexpected rebellion of his vassal, Akechi Mitsuhide.
Nobunaga only had a few guards and retainers with him when he was attacked, ending his Sengoku period campaign to unify Japan under his power. Nobunaga's death was avenged two weeks later when his retainer Toyotomi Hideyoshi defeated Mitsuhide in the Battle of Yamazaki, paving the way for Hideyoshi to complete the unification of Japan.
Mitsuhide's motive for assassinating Nobunaga is unknown, though there are multiple theories for his betrayal.
Context
By 1582, Oda Nobunaga was the most powerful daimyo in Japan and was continuing a sustained campaign of unification in the face of the ongoing political upheaval that characterized Japanese history during the Sengoku period. Nobunaga had destroyed the Takeda clan earlier that year at the Battle of Tenmokuzan and had central Japan firmly under his control, with his only rivals, the Mōri clan, the Uesugi clan, and the Hōjō clan, each weakened by internal affairs. After the death of Mōri Motonari, his grandson Terumoto strove only to maintain the status quo, aided by his two uncles, as per Motonari's will. Hōjō Ujiyasu, a renowned strategist and domestic manager, had also died, leaving his less prominent son Ujimasa in place. The death of Uesugi Kenshin left the Uesugi clan devastated also by an internal conflict between his two adopted sons, weaker than before. The nearly decade-long Ishiyama Hongan-ji War also had already ended with the conclusion of peace.
It was at this point that Nobunaga began sending his generals aggressively in all directions to continue his military expansion. Nobunaga ordered Hashiba Hideyoshi to attack the Mōri clan in the chūgoku region; Niwa Nagahide to prepare for an invasion of Shikoku; Takigawa Kazumasu to watch the Hōjō clan from Kōzuke Province and Shinano Province; and Shibata Katsuie to invade Echigo Province, the home domain of the Uesugi clan.
Nobunaga, confident of unifying the country after destroying the Takeda clan, returned to Azuchi in high spirits. Tokugawa Ieyasu also came to Azuchi Castle to thank Nobunaga for giving him the Suruga province. However, around this time, the Mōri clan launched a large-scale counteroffensive in the Chūgoku region, and Nobunaga received a request for reinforcements from Hashiba Hideyoshi, whose forces were stuck besieging the Mōri-controlled Takamatsu Castle.
Nobunaga immediately ordered Akechi Mitsuhide to go to the Chugoku region to support Hideyoshi, and he himself was to follow soon after. Nobunaga began his preparations and headed for Honnō-ji temple in Kyoto, his usual resting place when he stopped by in the capital. Ieyasu was advised by Nobunaga to go sightseeing in the Kansai region, such as Kyoto and Osaka, so he parted ways with him and left for Sakai.
Nobunaga was unprotected at Honnō-ji, deep within his territory, with the only people he had around him being court officials, merchants, upper-class artists, and dozens of servants. Nobunaga had only a small force with him, and all the generals under his command were fighting hard in various parts of the country. Taking advantage of this opening, Mitsuhide Akechi suddenly turned against Nobunaga.
Akechi's treachery
Upon receiving the order, Mitsuhide returned to Sakamoto Castle and moved to his base in Tanba Province. Around this time, Mitsuhide had a session of renga with several prominent poets, where he made clear his intentions of rising against Nobunaga. Mitsuhide saw an opportunity to act, when Nobunaga was not only resting in Honnō-ji and unprepared for an attack, but all the other major daimyō and the bulk of Nobunaga's army were occupied in other parts of the country. Mitsuhide led his army toward Kyoto under the pretense of following the order of Nobunaga. It was not the first time that Nobunaga had demonstrated his modernized and well-equipped troops in Kyoto, so the march toward Kyoto did not raise any suspicion from Mitsuhide's men. Before dawn, Mitsuhide, leading 13,000 soldiers, suddenly changed course in the middle of his march and attacked Honnō-ji Temple, where Nobunaga was staying.