Stories of the Japanese 01200 [End of the Northern and Southern Courts Period] The First Rebellion of Oyama Yoshimasa

May 16, Tenju 6 / Koryaku 2 (1380). In Mogahara, Shimotsuke Province (Utsunomiya City, Tochigi Prefecture), Oyama Yoshimasa (?: ?-1382) engaged in battle with Utsunomiya Mototsuna (1350-1380), driving Mototsuna to his death. The cause is not well understood, but it is believed there was a territorial dispute.
Utsunomiya Mototsuna was the son of Utsunomiya Tsunatsuna, who had previously led the "Taira Uprising," and was a hostile force to the Kamakura Shogunate.
On the other hand, regarding the Oyama family, while the head of the family, Tomosato, sided with the Southern Court, his younger brother Ujimasa (1329-1355) sided with the Northern Court, leading to a deepening conflict that Kitabatake Chikafusa even referred to as a "fratricidal war" in his letters. However, after Tomosato's death, Ujimasa succeeded as the head of the family, bringing the entire family to the Northern Court side, and subsequently, they became part of the Takauji faction. After Ujimasa's death, his heir, Yoshimasa, succeeded as the head of the family.
In other words, since Oyama Yoshimasa was part of the Takauji faction, he was nominally an ally from the perspective of the Kamakura Shogunate, but emotionally, he was considered a hostile force. The conflict between Utsunomiya and Oyama was, therefore, a struggle between hostile forces.
Kamakura Kubo Ujimitsu, who followed the lineage of the Tadayoshi faction, likely thought he would crush the Oyama family if given any excuse. Citing the fact that Yoshimasa had ignored orders to cease hostilities and attacked the Utsunomiya family, Ujimitsu issued an order to suppress Oyama Yoshimasa. Furthermore, he set out from Kamakura on June 15 to personally lead the suppression of Oyama, heading toward Oyama (Oyama City, Tochigi Prefecture).
Starting with a battle at the north gate of Gion Castle (Oyama City, Tochigi Prefecture), Yoshimasa's residence, on August 9, Ujimitsu's side began a relentless series of attacks.
・August 12: Battle of Daishoji Encampment
・August 16: Battle inside Gion Castle
・August 23: Battle of Tenno Gate
・August 29: Battle of the West Gate of Yoshimasa's Residence
Although the details of the battles are not recorded, it can be said that these were attacks that continued day after day.
On September 19, Ujimitsu finally ceased his attacks after receiving notification from Oyama Yoshimasa that he would surrender.
However, the situation did not settle down yet. Although Oyama Yoshimasa himself should have appeared before Ujimitsu to apologize, he kept making excuses and did not come. Ujimitsu's distrust of Yoshimasa continued to grow.
In the end, the suppression of Yoshimasa was decided once again in January of the following year, and the fighting up to this point is known as the "First Rebellion of Oyama Yoshimasa."