Hōjō Ujitsuna was the son of Hōjō Sōun, founder of the Go-Hōjō clan. He continued his father's quest to gain control of the Kantō (the central area, today dominated by Tokyo, of Japan's main island).In 1524, Ujitsuna took Edo Castle, which was controlled by Uesugi Tomooki, thus beginning a long-running rivalry between the Hōjō and Uesugi families. Two years later, the Uesugi attacked and burned Kamakura, which was a major loss to the Hōjō symbolically, because the earlier Hōjō clan from which they took their name fell in the siege of Kamakura in 1333.