was originally before becoming a monk. Due to his red complexion, he was sometimes known as Aka-nyūdō, "the Red Monk". He was one of the shogun daimyōs who fought against Hosokawa Katsumoto during the Ōnin War in Heian-kyō.
Biography
Yamana Sōzen was born to Yamana Tokihiro (1367–1435), head of the Yamana clan. Tokihiro was the shugo (provincial governor) of Tajima, Bingo, Aki, and Iga provinces. Tokihiro, who was often in bad health, retired in 1433 and passed his numerous lands to Sōzen. Sōzen went on to defeat Akamatsu Mitsuhide (1373–1441) of Akamatsu clan in the Kakitsu Incident, and became governor of Harima Province the same year.
In 1464, a succession dispute erupted over the shogunate itself. The shōgun, Ashikaga Yoshimasa, was considering retirement. Hosokawa supported the Shōgun's brother, Ashikaga Yoshimi as the successor. Hino Tomiko, who was the mother of Ashikaga Yoshihisa, was against her husband's decision to give the shogunate to Yoshimi, so she sought military support to secure the succession of her son Yoshihisa. Yamana chose to support Yoshihisa, the Shōgun's infant son.