Battle of Mayi The Battle of Mayi ( 馬邑之戰 ) was an abortive ambush operation by the Han Dynasty against the invading Xiongnu forces ; casualties were minimal . It marked the end of " de jure " peace between the Han Dynasty and Xiongnu , and stimulated the use of effective cavalry forces and offensive military policies by the Han court . Background . Before the Battle of Mayi , there had been two main encounters between the Chinese and the Xiongnu . During the Warring States period , General Li Mu of the State of Zhao defeated the Xiongnu by luring them deep inside Zhao territory and ambushing them . With similar tactics , General Meng Tian of the Qin Dynasty drove the Xiongnu north for 750 km and built the Great Wall to guard against future raids . After the humiliating defeat of Emperor Gao by Modu Shanyu at Baideng in 200 BC , the Han Dynasty was forced to resort to political appeasement in order to decrease the scale of Xiongnu hostility . However , despite the periodic gifts and heqin ( " marriage alliance " ) , border townships and villages were still ravaged by nomads , as the prosperous Chinese lands never failed to attract Xiongnu raids . After seven decades , Han Dynasty had built up its strength . Emperor Wu maintained a policy of peace early in his reign , but the court began to formulate ideas of striking a major blow against the Xiongnu . The traditional Chinese strategy was to lure the Xiongnu cavalry into Chinese territory , onto terrain where the Chinese army , composed almost entirely of infantry and chariots , would be at an advantage . The ambush . In 133 BC , at the suggestion of Wang Hui , the minister of vassal affairs , Emperor Wu had his army set a trap for the Xiongnu Shanyu at the city of Mayi . A powerful local trader / smuggler , Nie Wengyi ( 聶翁壹 ; also known as Nie Yi ( 聶壹 ) ) , deceptively claimed to Junchen Shanyu that he had killed the local magistrate and was willing to offer the city to the Xiongnu . The plan was to entice the Shanyu ' s forces into advancing on Mayi so that a Han force 300 , 000 strong , hidden around the area , could ambush them . The plan failed , ironically , because the Han ambush was made to look too attractive . When the Shanyu took the bait and moved in for a raid on Mayi , he saw fields full of cattle but with no herdsmen . Feeling increasingly suspicious , the Shanyu ordered his men to halt their advance . Xiongnu scouts then captured a Han soldier from a local outpost , who disclosed the entire plan to the Shanyu . Shaken , the Shanyu then withdrew quickly before the Han forces could act . The Han forces were scattered at this point , unable to concentrate in time to catch the Xiongnu . Wang Hui himself , the commander of the entire Han operation , had only 30 , 000 troops under his direct command , too few to stop the Xiongnu from retreating to the steppe , or to defeat them . Wang hesitated and ordered the Han forces not to pursue . As a result , neither side suffered any casualties . Aftermath . Back at the imperial court , Wang Hui ' s political enemies blamed him for the plan ' s failure and his reluctance to pursue the retreating Xiongnu army . He was imprisoned . While awaiting trial , he bribed the powerful prime minister Tian Fen ( Emperor Wu ' s uncle ) in the hope of obtaining a parole . Emperor Wu still refused to spare Wang , who then committed suicide in prison . Though border military clashes had already continued for decades between the two sides , this " battle " ended the " de jure " " peace " between the Han and Xiongnu . The ambush operation revealed the Han Dynasty ' s hawkish stance , and the " marriage / gift for peace " policy was officially abandoned . For the next few years , Xiongnu would increase their border attacks , further solidifying the cause of pro - war factions and their control in the Han court . The result of the battle made Emperor Wu realize the difficulty for Han infantry to achieve superiority against the more mobile Xiongnu cavalry . This led to a change in Han strategy and hastened the development of an effective Han cavalry . In later campaigns , the Han dynasty went from a defensive stance to an offensive strategy of launching expeditions deep into Xiongnu territory . The failure of the Mayi operation also prompted Emperor Wu to reconsider his choice of commanders . Disappointed at the ineffectiveness of existing generals , Emperor Wu began to look for younger generations of military hopefuls capable of offensive anti - cavalry warfare . This led to the rise of famous new - generation tacticians like Wei Qing and Huo Qubing , and decline in favour for traditional commanders like Li Guang .