Siege of Odawara (1590): Hideyoshi Completes Japan's Unification

The Siege of Odawara was the campaign of 1590 in which Toyotomi Hideyoshi surrounded the castle of the Later Hōjō clan in Sagami Province and forced its surrender. The fall of the Hōjō, who had dominated the Kantō plain for nearly a century, removed the last great independent power in Japan and effectively completed the country’s unification under Hideyoshi.

Background: the Hōjō and Hideyoshi

The Later Hōjō clan was founded by Ise Shinkurō, known as Hōjō Sōun, who seized Odawara around 1495. Over five generations his descendants built a well-run domain covering much of the Kantō, with Odawara as its fortified capital. By 1590 the clan was led by Hōjō Ujinao, though real influence remained with his father, Ujimasa.

After the death of Oda Nobunaga in 1582, Hideyoshi had subdued central Japan, Shikoku (1585) and Kyushu (1587). He demanded that the Hōjō come to Kyoto and submit. The Hōjō sent envoys but delayed a personal visit by Ujimasa, and a dispute with the Sanada clan over Numata in Kōzuke Province was referred to Hideyoshi for judgement.

In late 1589 a Hōjō retainer seized Nagurumi Castle, which Hideyoshi’s ruling had left to the Sanada. Hideyoshi treated this as a breach of his ban on private warfare and declared war on the Hōjō.

The campaign

Hideyoshi assembled one of the largest armies in Japanese history, commonly estimated at between 150,000 and 220,000 men, together with a fleet that blockaded the coast. Among his commanders were Tokugawa Ieyasu, whose lands bordered the Hōjō, as well as Maeda Toshiie and Uesugi Kagekatsu in the north. Hideyoshi left Kyoto in the spring of 1590.

The Hōjō chose to defend their castles rather than fight in the field. Odawara was protected by a vast outer earthwork, the sōgamae, which enclosed the town and ran for roughly nine kilometres. The plan was to wait until the besiegers ran short of supplies, as earlier attackers of Odawara had done.

Hideyoshi’s army stormed Yamanaka Castle in the Hakone mountains in a single day and then surrounded Odawara from about early May. Other forces reduced the network of Hōjō branch castles across the Kantō. Hachiōji Castle fell after a fierce assault in July, while Oshi Castle resisted Ishida Mitsunari’s attempt to flood it and held out until after Odawara itself had surrendered.

Life in the siege camp

Hideyoshi treated the siege as a show of power and permanence. He brought his consort Yodo-dono, tea masters including Sen no Rikyū, and entertainers, and his officers built houses and gardens around their camps. Markets sprang up to supply the army.

On a hill south-west of Odawara he built Ishigakiyama Castle, the first stone-walled castle in eastern Japan. Tradition says trees concealed it until it was complete and were then felled, so it seemed to appear overnight; it is therefore known as the Ichiya-jō, or “one-night castle”. In reality the work took about eighty days.

Lords who had not yet submitted came to Odawara to do so. The most famous was Date Masamune of the north-east, who arrived late, in the summer of 1590; according to a well-known tradition he appeared in white robes to show he was ready to die, and Hideyoshi pardoned him.

Surrender

Isolated and with no hope of relief, the Hōjō leaders debated for weeks without agreeing on a course, giving rise to the Japanese expression “Odawara hyōjō” for an endless and fruitless meeting. Ujinao finally surrendered on the 5th day of the 7th month, 4 August 1590 in the Gregorian calendar.

Hideyoshi ordered Ujimasa and his brother Ujiteru to commit suicide, which they did a few days later. Ujinao, who was married to a daughter of Ieyasu, was spared and exiled to Mount Kōya; he died in 1591.

Consequences

Hideyoshi gave the former Hōjō lands in the Kantō to Tokugawa Ieyasu in exchange for his home provinces. Ieyasu moved his headquarters to the small castle town of Edo, the future Tokyo, which became the base from which his family would later rule all of Japan. Hideyoshi then marched north to Aizu and reorganised the lords of north-eastern Japan, and by 1591 the whole country acknowledged his authority.

With unification complete, Hideyoshi soon turned his ambitions abroad, launching the invasion of Korea in 1592.

Timeline

• c. 1495: Hōjō Sōun takes Odawara.
• 1589, late: A Hōjō retainer seizes Nagurumi Castle; Hideyoshi declares war.
• 1590, spring: Hideyoshi’s army marches east; Yamanaka Castle falls in one day.
• 1590, from about May: Odawara is besieged by land and sea.
• 1590, July: Hachiōji Castle falls; Ishigakiyama Castle is completed.
• 1590, 4 August: Hōjō Ujinao surrenders.
• 1590, August: Ujimasa and Ujiteru commit suicide; Ieyasu receives the Kantō.
• 1591: Ujinao dies on Mount Kōya; Hideyoshi’s rule is acknowledged nationwide.

Why it matters

The fall of Odawara ended the Sengoku period’s last great regional power and made Hideyoshi master of all Japan. Its most lasting consequence was unintended: by moving Tokugawa Ieyasu to Edo, Hideyoshi placed his most powerful rival in a rich and secure base, from which the Tokugawa would rise to rule Japan for more than 250 years.