Nobunaga was angered by the takeover of land belonging to both Iwamura Castle and Naegi Castle after the death of the Toyama brothers.
In October of the third year of the Genki era (1572), Takeda Shingen suddenly launched an attack on the territories of the Tokugawa clan. For Oda Nobunaga and Uesugi Kenshin, it was a bolt from the blue. Nobunaga had been engaged in negotiations for a peace settlement between Shingen and Kenshin, along with Shogun Ashikaga Yoshiaki. They were on the verge of reaching an agreement. Interestingly, rumors had been circulating that Takeda Shingen would attack Uesugi, and Nobunaga had just requested Takeda Shingen to exercise restraint and received his agreement.
Not only that, in January of the same year, the marriage proposal between Shingen’s daughter Matsuhime and Nobunaga’s heir, Nobutada, was in the final stages. There was no sign that Shingen would attack Oda Nobunaga and Tokugawa Ieyasu. It is presumed that Shingen’s decision to attack was based on the issue of the treatment of the Higashimino-Toyama clan.
In May of the same year, Toyama Kageto, lord of Iwamura Castle and his brother, Toyama Naokado, lord of Maegi Castle, died one after the other. The cause of their deaths is said to have been battle injuries sustained in a war with the Miki clan of Hida Province. This triggered civil strife within the Toyama clan, and Oda Nobunaga dispatched Oda Nobuhiro and Kawajiri Hidetaka to seize Iwamura Castle. Nobunaga placed the Toyama clan, known as the Seven Heads of Toyama, under his control, and deployed over 2,000 men to Gifu Castle during his absence.
The Toyama clan, at the time, maintained a neutral stance towards both the Takeda and Oda clans. However, the civil strife was perceived as an infringement by Nobunaga.
Due to Takeda Shingen’s suspicions towards Oda Nobunaga, who did not restrain Ieyasu, this became the decisive factor for severing ties.
Nobunaga, upon learning of Shingen’s invasion, expressed his anger, stating, “Shingen’s actions are unprecedentedly unjust and show a lack of samurai principles. From now on, I will never join hands with Shingen for all eternity”.
Oda Nobunaga was facing ongoing uprisings against his rule in the Kinai region, making it difficult for him to fully focus on dealing with Takeda.
Furthermore, in mid-October, the Toyama clan, in opposition to Nobunaga’s control over Iwamura, rebelled and declared their allegiance to the Takeda side in November. Shingen dispatched Shimojo Nobushi to Iwamura Castle on the 14th of the same month and successfully secured it. Finally, the Takeda clan’s influence began to cast its eyes on Gifu.
In front of Nobunaga’s eyes, the Takeda army faced a desperate situation and halted their activities.
After spending the New Year in the Osakabe, Tōtōmi province, the Takeda army invaded Mikawa in January of the fourth year of the Genki era (1573) and besieged Noda Castle ruled by Suganuma Sadamitsu and assisted by reinforcements such as Matsudaira Tadamasa. Ieyasu was unable to rescue Noda, and the castle surrendered in February.
The defeat at the Battle of Mikatagahara and the Takeda army’s invasion of Mikawa unsettled the shogun, Ashikaga Yoshiaki.
In February, the shogun Ashikaga Yoshiaki, publicly declared his opposition to the Oda clan and finally raised his army. Nobunaga’s crisis deepened even further. However, after the Takeda army captured Noda Castle, they halted their movements while entering Nagashino Castle. It is said that Shingen fell ill and his condition was critical.
Despite the fact that Nobunaga was in a desperate situation during February and March, the Takeda army did not make any further moves from Nagashino Castle.
In March, Shingen’s condition worsened, and the Takeda army decided to abandon the decisive battle with Oda Nobunaga and retreat to Shinano province.
Shingen instructed his son, Takeda Katsuyori, and his chief vassals as follows:
(1) to keep his death a secret for three years
(2) Succession of headship shall be granted to his grandson, Nobukatsu, but that Katsuyori would be in charge of the family until Nobukatsu grew up.
(3) Nobukatsu would inherit the headship when he reached the age of 16.
4) Katsuyori is forbidden to use the banner of Sun Tzu, the banner of Hachiman Daibosatsu, and the banner of Shogun Jizo. All of these are to be inherited by Nobukatsu.
(5) Katsuyori shall use only the “Dai” banner as before, but shall be allowed to wear the helmet of Suwa Hosshou, which shall be handed over to him after Nobukatsu inherit the headship.
(6) If Oda Nobunaga attacks, intercept him in a difficult mountainous region and make it an endurance battle, which would exhaust the forces in the Kinai region and force them to retreat.
(7) Lure Ieyasu deep into Suruga and defeat him.
(8) Seek peace with Uesugi Kenshin. Do not harm the young Katsuyori.
(9) There is no need for a funeral for himself. Dress him in armor and sink his body in Lake Suwa.
These were among the instructions left by Shingen.
Shingen passed away on April 12th of the fourth year of the Genki era (1573) in Komaba, Shinano Province. He was 53 years old.
