Because of the Choukyou War (1487 - 1505), a conflict between the Yamanouchi Uesugi clan and the Ogigayatsu Uesugi clan, who controlled the western half of the Kanto region, the military forces of both clans were depleted. The Odawara-Hojo clan seized the opportunity to begin conquering territory in Kanto from the south, as if substituting the rulers.
On January 13, 1524, Ujitsuna, the second head of the Hojo clan, took control of Edo Castle, taking advantage of the absence of Uesugi Tomooki, the lord of Edo Castle, with assistance from the castle keeper Ota Suketaka and his brother Sukesada, claiming the Edo region.