 In 430 BC, Yiqu invaded Qin territory, forcing Duke Zao of Qin to abandon lands north of lower Wei River.The following three decades were the pinnacle of Yiqu power, with its territory doubling to almost .At this point, Yiqu had become a major threat to Qin, who had to solely focus on dealing with this north-western neighbour and thus became marginalised by other major Central Plain vassals states to the east.