 Wang Jun then killed He Yan and regained control of You.He and his allies Sima Teng, Duan Wuwuchen of the Duan Xianbei clan, and the Wuhuan then attacked Sima Ying in southern Hebei.Sima Ying permitted Liu Yuan, an ethnic Xiongnu commander to leave Ye in southern Hebei and return to Shanxi to mobilize the Xiongnu folk for this war.