Battle of Okehazama
In 1560, Yoshimoto was killed in the Battle of Okehazama, the province of Totomi and Mikawa went into chaos. Ujizane succeeded his father, but due to the chaotic state of the Imagawa clan, many vassals betray Ujizane. His grandmother, Jukei-ni, who exercised great political power, died in 1568. Motivated by this, Takeda Shingen and Tokugawa Ieyasu attacked the lands of Imagawa.