The Battle of Itsukushima: How Motonari Broke Sue Harukata's Great Army

On September 30, 1555 (Kōji 1), at Itsukushima (the modern Miyajima in Hatsukaichi City, Hiroshima Prefecture) in Aki Province, Mōri Motonari mounted a surprise attack on Sue Harukata's great army and drove Harukata to his death.

This engagement, later called the 'Battle of Itsukushima,' was the largest turning point of Motonari's life and laid the foundation for the subsequent Mōri conquest of ten provinces of the Chūgoku region.

It is counted as one of the Three Great Surprise Attacks of Japan (Okehazama, Itsukushima, Kawagoe Night Battle).

In 1551 (Tenbun 20), Ōuchi Yoshitaka of Suō was driven to suicide by his retainer Sue Harukata (then Sue Takafusa) in a coup.

Harukata, who substantially took over the Ōuchi house, sought to bring the kokujin lords of the surrounding region, including Mōri Motonari, under his control.

Motonari initially showed the posture of submitting to Harukata, but from a struggle for initiative within Aki Province he broke with Harukata in 1554 (Tenbun 23) and entered a state of confrontation in the vicinity of Itsukushima.

A decisive engagement between the two had become a matter of time.

The core of Motonari's strategy was to draw the Sue army into the confined terrain of Itsukushima.

Itsukushima is an island of about ten kilometers north-south by five kilometers east-west, with little flat ground and unsuited to the deployment of a great army.

Motonari spread false information to Harukata that the Miyanoo Castle on Itsukushima was strategically important, and induced Harukata himself to land on the island with his great army.

Although suspicious of Motonari's intent, Harukata landed on the island to attack Miyanoo Castle and placed his headquarters there.

The troop numbers at the Battle of Itsukushima are told as a famous 'force disparity' even among Sengoku-period battles.

Tradition gives Sue's force as 20,000 to 30,000 and the Mōri force as 4,000 to 5,000.

But Sengoku-period troop number records vary widely between sources, and the position of recent scholarship is that fixing the actual numbers is difficult.

What can certainly be said is that the Sue army was great in number, and the Mōri army was inferior.

Given the terrain of Itsukushima, the actual combat force of the Sue army that could land may have been smaller than the tradition gives.

On the night of September 30, 1555 (old calendar), in a storm, Motonari led his main army and landed on Itsukushima from the northern Tsutsumigaura.

At the same time a separate force under Kobayakawa Takakage came around from the west, and as dawn broke they struck the Sue headquarters from behind.

The Sue army, taken by surprise, fell into confusion, was unable to mount an effective counterattack, and broke; Harukata fled from Tō-no-Oka (the modern Miyajima) to Ōe-no-Ura and finally took his own life.

The engagement itself was decided in half a day. Motonari's precise plan and the use of the storm are recorded as the causes of victory.

What made the landing on Itsukushima possible was the cooperation of the Inland Sea pirate confederation, the Murakami navy (the three houses of Innoshima, Nōshima, and Kurushima).

Motonari negotiated with the Murakami navy in advance and requested the surprise crossing to Itsukushima and the sea blockade.

With the Murakami navy cutting off the Sue army's seaborne supply and line of retreat, the pursuit after the battle functioned perfectly.

Motonari's diplomatic skill in cleverly incorporating the maritime power of the Inland Sea made the victory certain.

Motonari, having toppled Sue Harukata at Itsukushima, brought the former Ōuchi territory into his hand at once and established a great domain centered on Aki, Suō, and Nagato.

Before this the Mōri had been only a powerful kokujin house of Aki Province, but from this battle on they rose to become a principal power of the Chūgoku region, expanding within ten years to rule over ten provinces.

The battle of fifty-eight-year-old Motonari became a historical event that changed the pattern of Sengoku-period headship transition and power expansion.

The modern Itsukushima (Miyajima) is known as a tourist destination housing the world cultural heritage site of Itsukushima Shrine, but the remains of the battlefield of the Battle of Itsukushima also survive.

Tō-no-Oka, Ōe-no-Ura, Tsutsumigaura, and other tradition sites and signboards remain.

Motonari, who triggered the unprecedented matter of combat on a sacred island, is recorded as having performed large-scale memorial services and donations to Itsukushima Shrine after the battle.

One sees a political consideration that resolved the religious problem of combat in a divine precinct by lavish protection after the fact.