Tanemune was named the shugô of Mutsu province in 1522. He composed the Date family House Code, the Jinkaishu, in 1536. Soon afterwards he intervened on behalf of the Ôsaki family, who were suffering internal strife and thereby brought them under his influence by giving his second son as heir to that house. In 1542 Tanemune announced his intention to send his 3rd son Sanemoto to be adopted by the Uesugi, a plan his heir, Harumune, strongly opposed. The antagonism between Tanemune and Harumune escalated into what is called the Tenbun no ran, in which the Date retainers and neighboring clans lined up behind one or the other. Tanemune enjoyed an initial advantage but, eventually, and with the aid of the Sôma and Ashina families, Harumune gained the upper hand and in 1548 Tanemune was compelled to retire in favor of Harumune. The Tenbun no ran, however, had created rifts within the Date retainer band that would linger for years and left the Date much weakened.
His daughter was the wife of Sôma Akitane.
Sons: Harumune, (Ôsaki) Yoshinori, Sanemoto, Munemoto, (Kasai) Harutane, Tsunamune
References
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005