The Sôma of Mutsu province were descended from Taira no Masakado (d.940). They supported Ashikaga Takauji in the early Nambochuko Period and were reasonably powerful in Mutsu at the start of the Sengoku Period. They clashed frequently with the Date clan - perhaps as many as 30 times over the course of 50 or so years, at times allying with other local families. Their last conflict occurred in 1589, and ended with the Sôma defeated by Date Masamune. Nonetheless, the advent of Toyotomi Hideyoshi in 1590 allowed the family to maintain their independent status. In 1600 Sôma Yoshitane was slow in responding to Tokugawa Ieyasu's summons to fight the Western forces, and as a result was deprived of his domain. On the occasion of the birth of Tokugawa Iemitsu in 1603, however, the Sôma were forgiven and were reinstated as daimyô. They were granted the 60,000 koku domain of Sôma Nakamura han in Iwashiro province, and remained there until the end of the Edo Period. The Sôma line died out at one point, but was able to continue as Katsutane (later Tadatane), second son of Tsuchiya Tadanao, was adopted into the family and married to a Sôma daughter.
- Arai Hakuseki, Joyce Ackroyd (trans.), Told Round a Brushwood Fire, University of Tokyo Press (1979), 280n21.