Chu–Han Contention in the context of "Eighteen Kingdoms"

The Han dynasty was an imperial dynasty of China (202 BC – 9 AD, 25–220 AD) established by Liu Bang and ruled by the House of Liu. The dynasty was preceded by the short-lived Qin dynasty (221–206 BC) and a warring interregnum known as the Chu–Han Contention (206–202 BC), and it was succeeded by the Three Kingdoms period (220–280 AD). The dynasty was briefly interrupted by the Xin dynasty (9–23 AD) established by the usurping regent Wang Mang, and is thus separated into two periods—the Western Han (202 BC – 9 AD) and the Eastern Han (25–220 AD). Spanning over four centuries, the Han dynasty is considered a golden age in Chinese history, and had a permanent impact on Chinese identity in later periods. The majority ethnic group of modern China refer to themselves as the "Han people" or "Han Chinese". The spoken Chinese and written Chinese are referred to respectively as the "Han language" and "Han characters".

The Han emperor was at the pinnacle of Han society and culture. He presided over the Han government but shared power with both the nobility and the appointed ministers who came largely from the scholarly gentry class. The Han Empire was divided into areas directly controlled by the central government called commanderies, as well as a number of semi-autonomous kingdoms. These kingdoms gradually lost all vestiges of their independence, particularly following the Rebellion of the Seven States. From the reign of Emperor Wu (r. 141–87 BC) onward, the Chinese court officially sponsored Confucianism in education and court politics, synthesized with the cosmology of later scholars such as Dong Zhongshu.

The Han–Xiongnu Wars or Sino-Xiongnu Wars, were a series of military conflicts fought from 133 BC to 89 AD between the agrarian Chinese Han Empire and the nomadic Xiongnu confederacy, although extended conflicts can be traced back as early as 200 BC and as late as 188 AD.

The Chinese civilization initially clashed with Inner Asian nomadic tribes (then collectively known as Di) that would later become the Xiongnu during the Warring States period, and various northern states built elongated fortifications (which later became the Great Wall) to defend against raids down from the Mongolian Plateau. The unified Qin dynasty, who conquered all other states under Emperor Qin Shi Huang, dispatched General Meng Tian in 215 BC in a successful campaign to expel the Xiongnu from the Ordos region (which was often used as a staging area to threaten Qin's Guanzhong heartland). However, the subsequent civil wars following the Qin dynasty's collapse gave the Xiongnu tribes, who were then unified into a large confederacy under Modu Chanyu, the opportunity to reinvade the Ordos region. After the Han dynasty was established in 202 BC, Emperor Gao tried to fight off Xiongnu invasions but had himself trapped in an ambush during the Battle of Baideng, and a truce was negotiated by bribing Modu's wife, thus ending first Han–Xiongnu War. Decades of de jure peace then followed with the Chinese gifting "harmony via marriage" to appease the Xiongnu, who still routinely raided Chinese borderlands.

Xiang Yu (c. 232 – c. January 202 BC), born Xiang Ji, was a Chinese warlord who founded and led the short-lived kingdom-state of Western Chu during the interregnum period between the Qin and Han dynasties known as the Chu–Han Contention (206–202 BC). A nobleman of the former state of Chu, Xiang Yu rebelled against the Qin dynasty under the command of his uncle Xiang Liang, and was granted the title of "Duke of Lu" (魯公) by King Huai II of the restoring Chu state in 208 BC. The following year, he led an outnumbered Chu army to victory at the Battle of Julu against the Qin armies led by Zhang Han. After the fall of Qin, Xiang Yu divided the country into a federacy of Eighteen Kingdoms, among which he was self-titled as the "Hegemon-King of Western Chu" (西楚霸王) and ruled a vast region spanning central and eastern China, with Pengcheng as his capital.

Although a formidable warrior and tactician, Xiang Yu was poor in both diplomacy and strategy, especially after dismissing his own adviser Fan Zeng. He was later outcompeted by his main rival Liu Bang during the massive civil war among the rebel kingdoms, which concluded with his eventual defeat and suicide in a last stand at the Battle of Gaixia. The demise of Xiang Yu allowed Liu Bang to subsequently become the founding emperor of the newly established Han dynasty, which is widely regarded as a golden age in Chinese history.