During the Warring States period (475–221 BC) Chu became the major adversary of the upstart State of Qin to the northwest (in what is now Guanzhong, Shaanxi province), which began to assert itself by outward expansionism. As wars between Qin and Chu ensued, Chu lost more and more land: first its dominance over the Sichuan Basin, then (in 278 BC) its heartland, which correspond to modern Hubei. In 223 BC Qin chased down the remnants of the Chu regime, which had fled eastwards, as a part of Qin's wars of uniting China.