He gained control of Izu Province in 1493, avenging a wrong committed by a member of the Ashikaga family which held the shogunate. With Sōun's successful invasion in Izu province, he is credited by most historians as being the first "Sengoku daimyō". After building a stronghold at Nirayama, Hōjō Sōun secured Odawara Castle in 1494, the castle which would become the center of the Hōjō family's domains for nearly a century. In an act of treachery, he seized the castle after arranging for its lord to be murdered while out hunting.