1566: The Surrender of Gassantoda Castle—The Fall of the Amago Clan
Mōri Motonari besieged the Amago stronghold of Gassantoda Castle for three years, and as supplies dwindled, the castle fell into chaos when its lord Amago Yoshihisa, deceived by Motonari's schemes, purged his own senior retainers. In November, Yoshihisa finally surrendered the castle, ending the Amago clan's rule over the San'in region as a daimyo house and leaving Motonari in control of nearly the entire Chūgoku region.
Events this year
Month 9
Takeda Shingen advanced his invasion of western Kōzuke and captured Nagano Narimori's Minowa Castle in September. The Nagano clan fell, and the castle became a base for Takeda rule in the region.
Sources 高崎市「箕輪城跡」／高崎市・笹本正治「箕輪城と武田氏」
After pacifying Mikawa, Matsudaira Ieyasu received court approval to adopt the Tokugawa name and was appointed governor of Mikawa, strengthening the legitimacy of his rule.