BBy 400 B.C.E. advances in military technology were undermining the old aristocratic social structure of the Zhou. Large, well-drilled infantry armies able to withstand and defeat chariot-led forces became potent military forces in the Warring States Period, which lasted from 403 B.C.E. to 221 B.C.E. Fueled by the development of new weaponry and war tactics, the Chinese states destroyed each other one by one until only one state was left standing — the state of Qin (chin).