Oyama Deliberation

The Oyama Deliberation was a war council convened by Tokugawa Ieyasu in what is now Oyama, Tochigi Prefecture, on the 25th day of the 7th month of Keichō 5 (1600). Eighteen years had passed since the Honnōji Incident, and the power struggle within the Toyotomi government had reached its peak. The council became the decisive turning point that led to the Battle of Sekigahara.

Background and Circumstances

In Keichō 3 (1598), on the 18th day of the 8th month, the taikō Toyotomi Hideyoshi died of illness at Fushimi Castle. The Five Elders and Five Commissioners system, established under Hideyoshi's last instructions, was meant to support the Toyotomi government, but its balance began to collapse almost immediately. Tokugawa Ieyasu, as the foremost of the Five Elders, pressed ahead with marriage negotiations with various daimyō. He was accused of violating Hideyoshi's last wishes, and he came into sharp conflict with the Five Commissioners, including Ishida Mitsunari. In Keichō 4 (1599), Maeda Toshiie died, and the weight that had restrained the daimyō disappeared. The confrontation between Mitsunari and Ieyasu then reached a stage where mediation was no longer possible.

In the 6th month of Keichō 5 (1600), Ieyasu ordered the daimyō to prepare for a campaign to subjugate Uesugi Kagekatsu of Aizu. Kagekatsu had refused to come to the capital and was strengthening his military within his territory, and this was treated as evidence of rebellion. On the 21st day of the 7th month, Ieyasu himself departed Edo with a large army and marched north toward Aizu. The Eastern Army generals who had gathered at Utsunomiya Castle were preparing to advance toward Aizu.

However, on the 17th day of the 7th month of the same year, following the uprising led by Ishida Mitsunari and Ōtani Yoshitsugu, the three commissioners (Maeda Gen'i, Mashita Nagamori, and Natsuka Masaie) sent the "Naifu Chigai no Jōjō," a list of charges impeaching Ieyasu, to the daimyō. On the 19th day, the Western Army began attacking Torii Mototada at Fushimi Castle, starting the Siege of Fushimi Castle. This changed everything at once. Upon learning of the Western Army's uprising, Ieyasu was forced to abandon the Aizu campaign and gather the daimyō at Oyama to decide how to respond.

Course of the Council

On the 25th day of the 7th month, Ieyasu is said to have summoned the Eastern Army generals at Oyama. The daimyō who gathered are said to have included Fukushima Masanori, Kuroda Nagamasa, Hosokawa Tadaoki, Katō Yoshiaki, Tōdō Takatora, and Asano Yoshinaga. Although they had been favored by the Toyotomi, they were personally at odds with Mitsunari. However, no primary source records the council in detail, and there are various theories about whether it took place and what it contained.

It is also said that groundwork had been laid in advance, but even at the council itself, Ieyasu displayed cautious yet decisive leadership. He first explained the situation and declared that each daimyō could decide for himself whether to advance or withdraw in response to the Western Army's uprising. By showing that those who wished to return home could do so, he is said to have paradoxically aimed to test the loyalty of the daimyō and keep them from leaving.

Fukushima Masanori was the first to pledge his loyalty to Ieyasu. He is said to have declared that he would follow him even though his wife and children in Ōsaka were being held as hostages. This became the spark, and one after another, the generals declared that they would join Ieyasu's campaign. In this way, the unity of the Eastern Army generals was firmly established, and the forces that had been headed toward the campaign against Uesugi turned to face west.

Historical Significance

The historical significance of the Oyama Deliberation is manifold. First, the council decided the course of the realm. Had many of the daimyō abandoned Ieyasu and returned home, the development of the Battle of Sekigahara would have been fundamentally different. If Ieyasu had been left to challenge the Western Army alone, he would have been at a military disadvantage, and it cannot be ruled out that he would have been pushed into a compromise peace negotiation.

Second, the council reflects Ieyasu's political skill. Rather than coercing the daimyō, he drew them to his side by staging voluntary decision-making. This anticipated the basic model of daimyō control in the later Edo shogunate. Binding the daimyō together through on (obligation) and gi (righteousness) is said to be a political philosophy that underlay more than 260 years of Tokugawa rule that followed.

Third, the council made the division of the Toyotomi-affiliated daimyō decisive. With Fukushima Masanori, Kuroda Nagamasa, and other Toyotomi loyalists siding with Ieyasu, the Western Army led by Ishida Mitsunari, though it had the character of an anti-Ieyasu coalition, came to have a fundamental weakness in its ability to draw people together.

Connection to Swords

The warlords who gathered at the Oyama Deliberation each carried renowned swords. Fukushima Masanori had been granted the spear Nihongō (one of the three great spears of Japan) by Toyotomi Hideyoshi. It is said that Mori Tomonobu, a retainer of the Kuroda, later won the spear in a drinking bout. Hosokawa Tadaoki was a tea master counted among Rikyū's Seven Disciples. He established a style of uchigatana koshirae known as Higo-goshirae, and he is also known for his beloved sword Kasen Kanesada. The Oyama Deliberation, where warriors of such caliber gathered, was also a place where the warrior culture and sword culture of the late Sengoku period were condensed.

Tokugawa Ieyasu himself had a deep interest in swords, and the number of famous swords handed down in the Tokugawa family is large. The sword he carried at the council was a symbol of both his authority as a warrior and his resolve. The determination he showed in this place led directly to the historical outcome of the unification of the realm.

Ieyasu also possessed an uchigatana and a wakizashi by Muramasa, and the uchigatana was handed down to the Owari Tokugawa family. The story that Ieyasu loathed Muramasa blades as cursed swords (yōtō) that brought misfortune upon the Tokugawa family is considered a later fabrication. Even at the Oyama Deliberation, the swords carried by each general were more than mere weapons. They functioned as proof of loyalty and resolve.

Later Impact

In the Battle of Sekigahara, the Eastern Army won. In Keichō 8 (1603), Ieyasu was appointed Sei-i Taishōgun, and the Edo shogunate was established. The Oyama Deliberation, as its starting point, is inscribed in the turning point of history. In present-day Oyama, Tochigi Prefecture, a monument marking the site of the Oyama Deliberation has been erected, and the event is passed down as a source of local historical pride.

This council goes beyond a mere war council. It is one of the most notable political scenes in Japanese history, where the consensus-based decision-making of warrior society intersected with the leadership of a clan head. Even today, it continues to attract strong interest from historians and enthusiasts. The later fates of the generals who attended the council also form a great drama of Japanese history. Fukushima Masanori became lord of the Hiroshima domain after Sekigahara but was later stripped of his domain. Kuroda Nagamasa received the Chikuzen Fukuoka domain, with 520,000 koku. Hosokawa Tadaoki moved to Buzen Province, and his descendants continued as lords of the Higo Kumamoto domain until the late Edo period. The swords of the generals who gathered at this council remain today in museums and private collections across the country, conveying the breath of that era to the present.