 With Liu Song forces unable to siege Pengcheng effectively, they were forced to withdraw in spring 467, making these populous provinces lost to the Northern Wei.In 479, Xiao Daocheng usurped the throne of Liu Song and became emperor of the new Southern Qi dynasty.Upon hearing the news, the Northern Wei emperor prepared to invade under the pretext of installing Liu Chang, son of Emperor Wen of Liu Song who had been in exile in Wei since 465 AD.