The Chu–Han Contention (楚漢相爭), also known as the Chu–Han War (楚漢戰爭), was an interregnum of civil wars in Imperial China between the fall of the Qin dynasty in 206 BCE and the establishment of the Han dynasty in 202 BCE.

After the Qin dynasty was overthrown, the empire was divided into the Eighteen Kingdoms ruled by enfeoffed rebel leaders and surrendered Qin generals according to arrangement by Xiang Yu, the hegemon warlord. Due to dissatisfaction among the rebels, wars and rebellions soon broke out, most prominently between two major powers – Xiang Yu and Liu Bang, who were the rulers of the Western Chu and Han kingdoms, respectively. Other kingdoms also waged war against Chu and Han and among themselves, but these were largely insignificant compared to the Chu-Han conflict. The wars ended with a total victory to Liu Bang at the Battle of Gaixia, during which Xiang Yu committed suicide after losing all his men in a last stand. Having subdued all rival contenders, Liu Bang subsequently proclaimed himself emperor of the newly established Han dynasty.

Towards the end of the Warring States period, the western state of Qin conquered the other six states – Hán, Zhao, Yan, Wei, Chu and Qi – and unified China under the Qin dynasty in 221 BCE, and King Zheng of Qin declared himself the First Emperor of China. After his untimely death during the fifth imperial tour in 210 BCE, the chief eunuch Zhao Gao conspired with chancellor Li Si to install the incompetent Prince Huhai as the new emperor, forcing the suicide of the then-heir apparent Prince Fusu and purging anyone deemed disobedient in the Qin court. Due to Huhai's corrupt rule, a massive uprising led by Chen Sheng and Wu Guang broke out in Dazexiang (modern day Yongqiao District, Anhui) in 209 BC, and lasted five months until Qin forces finally managed to crush the rebellion with a hastily organized army of penal troopers.

Although the Dazexiang uprising had failed, other rebellions erupted consecutively over the next three years. The leaders of these rebellions were either pretenders of the former six states conquered by Qin, their supporters who sought to revert China back to the political order of a pre-Qin federacy, or simply opportunists who exploited the chaos. Among them, the most notable one was Xiang Yu, who descended from an aristocrat family of Chu generals and initially followed the rebellion of his uncle Xiang Liang, wanting to revive the Chu state with the exiled King Huai II as its nominal ruler. Another notable Chu rebel leader was Liu Bang, a rural sheriff from Pei County who had formed his own rebel group with his associates, many of who like Liu were local civil servants within the Qin bureaucracy before the rebellion. Liu Bang, who came from a grassroots background, had initially joined the Xiang Liang, but quickly became a rebel leader on-par with the Xiang Clan within the Chu camp due to his personal charisma and willingness to befriend anyone as allies.

In August 208 BC, Xiang Liang, the supreme commander of the Chu rebels at the time, was defeated and killed in action at Dingtao by Zhang Han, a Qin general responsible for crushing the Dazexiang rebellion. In the fallout, Xiang Yu and Liu Bang relocated King Huai II from Xuyi to a new capital in Pengcheng (彭城; present-day Xuzhou, Jiangsu). In September, King Huai II ordered all the Chu leaders to attack different Qin fronts, promising them that anyone who first invaded Guanzhong, the heartland of the Qin dynasty, can lawfully claim the whole region as fief under the title "King of Guanzhong". Xiang Yu was assigned to the northern front initially as a deputy general under Song Yi, who took over the late Xiang Liang's post as supreme commander, but he soon mutinied and killed Song under the accusation of treasonous cowardice. Xiang Yu then led an outnumbered Chu forces to a surprise victory over Zhang Han's forces at the Battle of Julu, and after the battle controlled nine commanderies in the former Liang and Chu territories.

While the bulk of the Qin forces were up north fighting Xiang Yu at Julu, Liu Bang led his forces west into the Guanzhong region via the Wu Pass, facing minimal resistance along the way due to his clever use of diplomacy, bribery and surprise attacks against the demoralized Qin defenders. By October 207 BCE, his army had overcome the last significant resistance in Lantian and arrived at the outskirts of the Qin capital Xianyang. Meanwhile in the Qin royal court, Zhao Gao had committed treason by forcing King Huhai to commit suicide, and installed another prince Ziying as a puppet ruler. Ziying, however, hated Zhao Gao intensely and soon plotted with eunuchs to have him assassinated and his three clans exterminated. With Liu Bang's forces approaching unopposed, Ziying decided to surrender the capital, bringing an end to the Qin dynasty. Liu Bang treated Ziying respectfully and entered Xianyang peacefully, forbidding his troops from harming civilians and looting the capital, citing that the Qin people were also victims of the empire's tyrannical rule and thus should not be punished unjustly. He then publicly proclaimed that all harsh Qin laws were to be abolished except strict punishments for murder, harm and theft, earning him the love from Qin citizens. His deputy Xiao He also had all the Qin code of law, archives and government documents collected and relocated for preservation.

However, when Xiang Yu eventually arrived as well, he immediately besieged and captured the Hangu Pass garrisoned by Liu Bang's troops out of frustration that Liu Bang had the easier route and stole all the glory. Liu Bang was then pressured into ceding the Guanzhong region to Xiang Yu despite the earlier agreement between them. When Liu Bang personally visited to pay respect and apology, Xiang Yu also attempted to assassinate him at the Feast at Swan Goose Gate under the advise of Fan Zeng, but Liu Bang escaped thanks to his humble courtesy and Xiang Yu's indecisiveness when confronted by Liu Bang's brother-in-law Fan Kuai. Xiang Yu then entered Xianyang allowing his troops to pillage and plunder the city, ordered the burning of the Epang Palace, and had all the surrendered Qin royalties executed. Later, Xiang Yu forced Liu Bang to accept the enfeoffment of the remote, underdeveloped Bashu region (present-day Sichuan Basin), which was then used mainly as penal colonies for exiled criminals. After lobbying by Liu Bang's friend Zhang Liang, a Hán aristocrat widely respected among the rebels for previously attempting to ambush and assassinate the First Emperor in 218 BC, Xiang Yu reluctantly added the better developed Hanzhong Basin to Liu Bang's fiefs, arguing that it now fulfilled the promise of "King of Guanzhong" as Hanzhong was connected to the region via mountain passes within the Qinling Mountains. As Liu Bang's forces relocated into the new fief, Xiang Yu had his troops following them as "escort", and Liu Bang resorted to burning the gallery roads behind his convoy as a precautionary measure to prevent being attacked in the rear and as a diplomatic gesture of accepting Xiang Yu's arrangement to never return again.

Xiang Yu then divided the former Qin Empire into numerous regional states collectively known as the Eighteen Kingdoms, each ruled by either a rebel leader or a surrendered Qin general, with the Kingdom of Chu being the hegemon holding the nominal suzerain power over the other kingdoms. Xiang Yu also honoured King Huai II with a higher title, "Emperor Yi of Chu", and declared himself "Hegemon-King of Western Chu". Shortly after that, he exiled the figurehead Emperor Yi to Chen County (郴縣, present-day Chenzhou, Hunan), and secretly ordered his ally Ying Bu, the King of Jiujiang, to intercept and assassinate the emperor along the way.