Oda Nobunaga: Why Was He Killed at Honnoji on the Verge of Unifying Japan?

Before dawn on the second day of the sixth month of 1582, soldiers under Akechi Mitsuhide surrounded Honnoji, a temple in Kyoto. Inside was Oda Nobunaga, the most powerful warlord in Japan. Tradition says that only about a hundred attendants were with him that night.

According to Shincho Koki, a chronicle written by his retainer Ota Gyuichi, Nobunaga learned that the attackers were Akechi men and replied that nothing could be done. He fought with bow and spear, withdrew as the temple burned, and is said to have taken his own life. He was forty-nine by Japanese count. His body was never found.

A young heir once mocked as a great fool had risen in about thirty years to the center of power in Japan. Why was he killed, on the verge of unifying the country, by a vassal he had trusted with great responsibility? This article follows his life to approach that question.

At his father's funeral, usually dated to 1552, Nobunaga is said to have thrown incense at the altar and left. Some retainers began to favor his younger brother, Nobukatsu, as the family's heir.

In 1553 he met his father-in-law, Saito Dosan, at Shotokuji Temple and surprised Dosan's men by appearing in formal dress. He later took Kiyosu Castle, defeated his brother's supporters at Inō in 1556, and in the following year had Nobukatsu killed after summoning him to Kiyosu.

By 1559, after taking Iwakura Castle, Nobunaga controlled almost all of Owari. In the same year he travelled to Kyoto and met the shogun, Ashikaga Yoshiteru. The new master of Owari was already looking toward the capital.

Nobunaga allied with Matsudaira Motoyasu, later Tokugawa Ieyasu, who had broken away from the Imagawa. Around 1563 he moved his base to Mount Komaki, where excavations have found stone walls built with large rocks.

After capturing Inabayama Castle in 1567, he renamed the place Gifu and began to use a seal reading Tenka Fubu. The phrase was long explained as a declaration that he would conquer all of Japan by force.

Recent research often reads the word tenka, the realm, as the capital region around Kyoto and the order associated with the shogun, rather than the whole country. Read that way, the seal may express restoring order in the capital. Whether it announced nationwide conquest remains a question to handle carefully.

In 1570, during a campaign against the Asakura, Nobunaga's brother-in-law Azai Nagamasa turned against him, and Nobunaga escaped to Kyoto through the Kutsuki valley. Despite a victory at the Anegawa River, the Azai and Asakura survived, the Honganji temple took up arms, and a situation later called the encirclement of Nobunaga took shape.

Of the attack on Enryakuji on Mount Hiei in 1571, Shincho Koki says that temple buildings were burned and thousands were killed. Excavations, however, have confirmed burnt layers from this period in only some locations, and some researchers suggest the scale was smaller than the chronicle states.

In 1573 the death of Takeda Shingen removed a major threat. Nobunaga drove Yoshiaki out of Kyoto and destroyed the Asakura and Azai. Yoshiaki, however, continued to call on other lords to oppose him.

Nobunaga's longest opponent was the Honganji temple in Osaka. Supported in part by the Mori navy, it resisted for about ten years until a settlement in 1580 mediated by Emperor Ogimachi.

During this decade Nobunaga placed regional commanders over wide areas: Shibata Katsuie in Hokuriku, Hashiba Hideyoshi in the west and Akechi Mitsuhide in Tanba. After pacifying Tanba in 1579, Mitsuhide held positions on both sides of Kyoto.

In 1580 Nobunaga sent his senior retainer Sakuma Nobumori a letter of reprimand in nineteen articles and expelled him. Long service did not protect someone who failed to deliver results. Historians have suggested that this severity placed heavy pressure on other vassals.

In the fifth month, Mitsuhide was released from hosting Ieyasu at Azuchi and ordered to support Hideyoshi in the west. The well-known tale that Nobunaga scolded him over spoiled fish appears in later books and cannot be confirmed in contemporary records.

On the night of the first day of the sixth month, Mitsuhide left Kameyama and turned toward Kyoto. The phrase usually given as his order, that the enemy was at Honnoji, also spread through Edo-period books. One participating warrior later wrote that he thought they were going to attack Ieyasu.

Explanations of Mitsuhide's motive include personal grievance, ambition, the Shikoku problem and a hidden mastermind. The Shikoku theory gained attention after the Ishigai documents but is not decisive, and most mastermind theories lack firm evidence. Mitsuhide was defeated by Hideyoshi at Yamazaki on the thirteenth and died soon after.

The first factor was his exposure in Kyoto. With his senior commanders far away in Hokuriku, the west, the east and Shikoku, Nobunaga stayed at Honnoji with only a small escort. Mitsuhide was the one general with a large army nearby.

The second was the pressure on vassals; the third was Mitsuhide's changing position after losing his role in Shikoku and being sent to assist Hideyoshi. Few sources reveal his inner thoughts, so no single theory is decisive.

This article suggests that the very system that let Nobunaga expand so quickly also created an empty space around his base and anxiety among his vassals, giving Mitsuhide a single chance. What do you think moved Mitsuhide most?