Lou Huan 樓緩 was in the beginning a high minister of King Wuling of Zhao 趙武靈王 (r. 325-299). He strengthened the army of Zhao by integrating barbarian-syle cavalry units. Later on he became counsellor-in-chief of King Zhaoxiang of Qin 秦昭襄王 (r. 306-251). In this position he created an alliance with Zhao and Song 宋 against the powerful union of Qi 齊, Wei 魏 and Han 韓. Qin was badly defeated, and Lou Huan had to resign his post. A later effort to subdue Zhao proved successless.