<P> During the Warring States period, the Qin, Zhao, and Yan states conquered various nomadic territories inhabited by the Xiongnu and other Hu peoples . They strengthen their new frontiers with elongated wall fortifications . By 221 BC, the Qin ended the chaotic Eastern Zhou period by conquering all other states and unifying the entire nation . In 215 BC, Qin Shi Huang ordered General Meng Tian to set out against the Xiongnu tribes, situated in the Ordos region, and establish a frontier region at the Ordos Loop . Believing that the Xiongnu were a possible threat, the emperor launched a pre-emptive strike against the Xiongnu with the intention to expand his empire . Later that year (215 BC), General Meng Tian succeeded in defeating the Xiongnu and driving them from the Ordos region, seizing their territory as result . After the catastrophic defeat at the hands of Meng, Touman Chanyu and his followers fled far into the Mongolian Plateau . Fusu (Prince of Qin) and General Meng Tian were stationed at a garrison in Suide and soon began with the construction of the walled defenses, connecting it with the old walls built by Qin, Yan and Zhao states . The fortified walls ran from Liaodong to Lintao, thus enclosing the conquered Ordos region, safeguarding the Qin empire against the Xiongnu and other northern nomadic people . Due to the northward expansion, the threat that the Qin empire posed to the Xiongnu ultimately led to the state formation of the many tribes towards a confederacy . </P> <P> However, after the sudden death of Qin Shi Huang, the ensuing political corruption and chaos during the short reign of Qin Er Shi would lead to various anti-Qin rebellions, eventually bring about the collapse of the Qin Dynasty . A massive civil war then erupted between various reinstated states, with Liu Bang eventually victorious to establish the Han Dynasty . During the transitional years between Qin and Han, while the Chinese were mainly focused towards the interior of their nation, the Xiongnu took the opportunity to retake the territory north of the wall . The Xiongnu frequently led incursions to the Han frontier and had considerable political influence over the border regions . In response, Emperor Gaozu led a Han army against the Xiongnu in 200 BC, pursuing them as far as Pingcheng (present - day Datong, Shanxi) before being ambushed by Modu Chanyu's cavalry . His encampment was encircled by the Xiongnu, but Emperor Gaozu escaped after seven days . After realizing that a military solution was not feasible for the time being, Emperor Gaozu sent Liu Jing to negotiate peace with Modu Chanyu . In 198 BC, a marriage alliance was concluded between the Han and the Xiongnu, but this proved far from effective as the incursions in the frontier regions continued . </P> <P> By the reign of Emperor Wu, the Han empire was prospering and the national treasury had accumulated large surpluses . However, burdened by the frequent Xiongnu raids at the frontier of the Han empire, the emperor abandoned the policies of his predecessors to maintain peace with the Xiongnu early in his reign . In 136 BC, after continued Xiongnu incursions near the northern frontier, Emperor Wu had a court conference assembled . The faction supporting war against the Xiongnu was able to sway the majority opinion by making a compromise for those worried about stretching financial resources on an indefinite campaign: in an engagement along the border near Mayi, Han forces would lure Junchen Chanyu over with wealth and promises of defections in order to eliminate him and cause political chaos for the Xiongnu . Emperor Wu launched his military campaigns against the Xiongnu in 133 BC . </P> <P> In 133 BC, the Xiongnu forces led by the Chanyu were lured into a trap at Mayi, while a Han army of about 300,000 troops laid in ambush against the Xiongnu . Wang Hui (王 恢) led this campaign and commanded a force of 30,000 men strong, advancing from Dai with the intention of attacking the Xiongnu supply route . Han Anguo (韓安國) and Gongsun He (公孫 賀) commanded the remaining forces and advanced towards Mayi . Junchen Chanyu led his army of 100,000 men towards Mayi, but he became increasingly suspicious of the situation . When the ambush failed, because Junchen Chanyu realized he was about to fall into a trap and fled back north, the peace was broken and the Han court resolved to engage in full - scale war . In light of this battle, the Xiongnu became aware of the Han court's intentions to go to war . By that point the Han empire was long consolidated politically, militarily, and economically, and was led by an increasingly pro-war faction in the imperial court . </P>

Explain one example of how the xiongnu influenced han policy
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