pursue a routed army
Chasing the north is a Chinese idiom. The Pinyin is Zhu ī B ē nzh ú B ě I, which means to pursue the defeated enemy. It comes from the Han Dynasty Jia Yi's Guo Qin Lun.
The origin of Idioms
Han Jiayi's on crossing the Qin Dynasty: "chasing the subjugated and chasing the north, one million corpses." Li Ling's answer to Su Wu Shu in the Han Dynasty: "however, you still have to cut the flag of the general, chase the north, wipe out the trace and sweep away the dust, and kill the commander."
Idiom usage
His elite horse team, who came from the desert and pursued the north, was his strong point. Gao Yang's "jade seat and Pearl curtain" Volume I
pursue a routed army
sport with the wind and play with the moon -- seek pleasure - cháo fēng yǒng yuè
There is no time to cover your eyes - jí tíng bù xiá yǎn mù
Beaver to rat, ice to rope - yǐ lí zhì shǔ、yǐ bīng zhì shéng