宗氏
Alongside the Shōni clan, whose hereditary clan heads now regularly operated under Sō clan guidance, the Sō fought the Ōuchi numerous times across the Sengoku period (1467–1600), and later the Mōri and Ōtomo clans as well; the clan lost and regained their territory in Chikuzen province on Kyūshū many times over the course of the period. In the end, the downfall of the Shōni, marked by Shōni Fuyuhisa's 1559 defeat at the hands of Ryūzōji Takanobu, brought an end to the Sō clan's territorial aspirations on Kyūshū.