The upheaval resulted in the further weakening of central authority, and throughout Japan regional lords, or daimyo, rose to fill the vacuum. In the course of this power shift, well established clans such as the Takeda and the Imagawa, who had ruled under the authority of both the Kamakura and Muromachi bakufu, were able to expand their spheres of influence. There were many, however, whose positions eroded and were eventually usurped by more capable underlings. This phenomenon of social meritocracy, in which capable subordinates rejected the status quo and forcefully overthrew an emaciated aristocracy became known as gekokujō which literally means "the underling conquers the overlord." One of the earliest instances of this phenomenon was Hōjō Sōun, who rose from relatively humble origins and eventually seized power in Izu province in 1493. Building on the accomplishments of Sōun, the Late Hōjō clan remained a major power in the Kantō region until its subjugation by Toyotomi Hideyoshi late in the Sengoku period. Other notable examples include the supplanting of the Hosokawa clan by the Miyoshi, the Shiba clan by the Oda clan, and the Toki by the Saito. 264e15

(from wikipedia)