The Han dynasty ruled China from 202 BC to 220 AD, apart from Wang Mang’s Xin interlude of 9–23 AD, governing first from Chang’an (modern Xi’an) and then from Luoyang. At its height it controlled roughly 6 million km²: estimates compiled on Wikipedia’s list of the largest empires put the Western Han at about 6.0 million km² around 50 BC and the Eastern Han at up to 6.5 million km² around 100 AD, with other estimates as low as 4.2 million. Its first nationwide census, in 2 AD, registered 57,671,400 people, about a third of humanity by the historian Walter Scheidel’s estimate. The empire was ruled by the Liu family of its founder, Liu Bang, and it mattered for what it left behind: the name the majority Chinese people still use for themselves, the Silk Road through the Hexi Corridor, paper, and a bronze coin that stayed the standard until the Tang dynasty.
Liu Bang’s Victory at Gaixia and the Wei Valley Base
The Han grew out of a collapse. The Qin dynasty had unified the Warring States in 221 BC, but its authority fell apart within four years of the first emperor’s death, and China split into Eighteen Kingdoms loyal either to Xiang Yu of Chu or to Liu Bang, whom Xiang Yu had made prince of the small Hanzhong fief on the Han River in what is now southwest Shaanxi. That river gave the dynasty its name. Liu Bang defeated Xiang Yu at the Battle of Gaixia, in modern Anhui, in 202 BC and took the title of emperor; he is known as Emperor Gaozu.
Geography shaped his first decisions. Gaozu first ruled from Luoyang, but a soldier, Lou Jing, and the general Zhang Liang persuaded him to build his capital in the Guanzhong region, the Wei River valley that had been the Zhou and Qin heartland, because it could feed a large core population and was easy to defend behind its mountain rim. Chang’an had about 146,000 people in 195 BC, when work began on its walls.
The early state was only half centralised. Thirteen commanderies under direct rule, including the capital region, covered the western third of the empire, while the eastern two-thirds was split into ten semi-autonomous kingdoms granted to Gaozu’s commanders and relatives. Over the next decades, especially after the Rebellion of the Seven States, the kingdoms lost their autonomy. The northern frontier was weaker still. The nomadic Xiongnu confederation defeated the Han in 200 BC, and for two generations the court bought peace with marriage alliances and payments of tribute while raids continued.
Emperor Wu’s Push into the Hexi Corridor and Tarim Basin
Expansion came under Emperor Wu (r. 141–87 BC), who abandoned appeasement in 133 BC. In 121 BC Han armies expelled the Xiongnu from the Hexi Corridor, the narrow strip of oases in today’s Gansu Province, as far as Lop Nur. In 111 BC the court created four frontier commanderies there: Jiuquan, Zhangye, Dunhuang and Wuwei. Most people on this frontier were soldiers, but the court also forcibly moved peasant farmers, government-owned slaves and convicts to work the new land, alongside farmers, merchants and labourers who were encouraged to migrate.
The diplomat Zhang Qian, who died around 114 BC, had already travelled west for Wu and brought back the first official Chinese reports on Central Asia, including the Greco-Bactrian lands and Parthia. His accounts, compiled by the historian Sima Qian, pointed the court toward the oasis city-states of the Tarim Basin and toward the fast “heavenly horses” of Dayuan in the Ferghana Valley. When Dayuan refused to trade them and Han envoys were killed, the general Li Guangli fought the War of the Heavenly Horses in 104 and 102 BC, and the second expedition won. From about 115 BC to 60 BC Han forces contested the Tarim Basin with the Xiongnu, and in 60 BC the court set up the Protectorate of the Western Regions to handle the oases’ defence and foreign affairs. Caravans left China through the Yumen Pass west of Dunhuang, now part of the Silk Road World Heritage Site inscribed in 2014.
The south and northeast were conquered at the same time. A naval campaign annexed Nanyue in 111 BC, bringing in modern Guangdong, Guangxi and northern Vietnam. The Dian kingdom in Yunnan followed in 109 BC, and in 108 BC Han armies conquered Gojoseon in the northern Korean Peninsula and set up the Lelang and Xuantu commanderies.
Wars this large had to be paid for. In 117 BC the government nationalised the private salt and iron industries, and in 119 BC it introduced the wuzhu coin, weighing 3.2 g, which remained China’s standard coin until the Tang dynasty (618–907).
The Peak around 50 BC to 2 AD: 6 Million km² and 57.7 Million People
By the middle of the 1st century BC the Western Han reached from the Lelang commandery in Korea to the oases of the Tarim Basin, and from the Hexi Corridor south to Nanyue in northern Vietnam. The figure of about 6.0 million km² for around 50 BC comes from the political scientists Rein Taagepera and Peter Turchin; estimates for the whole Han period range from 4.2 to 6.5 million km², and the Tarim oases were loosely held through the protectorate rather than governed like the commanderies.
The census of 2 AD is the best snapshot of the peak. It counted 57,671,400 people in 12,366,470 households, the first nationwide count in Chinese history. The farming commanderies of the Yellow River plain were the core that the frontier garrisons, the walls and beacon towers of the Han section of the Great Wall were built to protect. The period also produced papermaking, the stern-mounted rudder, raised-relief maps and a seismometer that showed the direction of distant earthquakes.
Wang Mang and the Yellow River Floods of 3 and 11 AD
The first collapse began at court and was finished by the landscape. Wang Mang, nephew of the powerful Empress Dowager Wang Zhengjun, became regent, then acting emperor for a child heir, and in 9 AD declared his own Xin dynasty. His reforms, which outlawed slavery, redistributed land and introduced new currencies that debased the coinage, met fierce opposition. What broke his regime were massive floods around 3 AD and 11 AD. Silt had raised the bed of the Yellow River until it overwhelmed the flood works and split into two branches, one reaching the sea north of the Shandong Peninsula and one south of it. Han engineers managed to dam the southern branch only by 70 AD.
Thousands of displaced farmers joined bandit and rebel groups such as the Red Eyebrows, and in 23 AD a mob broke into the Weiyang Palace and killed Wang Mang. Liu Xiu restored the dynasty as Emperor Guangwu on 5 August 25 AD and moved the capital east to Luoyang, beginning the Eastern Han. Floods on this scale are what gave the river its name of China’s Sorrow.
The restored state recovered much of the old frontier. The Northern Xiongnu took the Tarim Basin in 63 AD, but the general Ban Chao won back the oases, enlisting the Kushan Empire against Kashgar, and in 91 AD he was made Protector General of the Western Regions. Buddhism arrived along the same routes: it is first mentioned in 65 AD, and the White Horse Temple was built outside Luoyang under Emperor Ming. Later Eastern Han scholars looked back on the reign of Emperor Zhang (75–88 AD) as the dynasty’s high point.
Eunuchs, Yellow Turbans and Cao Pi’s Usurpation in 220
The second decline came from inside the palace. From 92 AD, when Emperor He used the eunuch Zheng Zhong to break the Dou clan, eunuchs and the clans of empresses fought for control of child emperors. A financial crisis and a Qiang rebellion lasting from 107 to 118 AD drained the treasury. Under Emperor Huan, palace eunuchs had the official Li Ying and his associates from the Imperial University arrested on a dubious charge of treason, and in 167 AD they were barred from office for good, the start of the Partisan Prohibitions; under Emperor Ling (r. 168–189) top posts were openly auctioned.
In 184 AD two Taoist movements rose at once. The Yellow Turbans of the faith healer Zhang Jue spread across eight provinces and were crushed within a year, while Zhang Lu’s Five Pecks of Rice movement in northern Sichuan and southern Shaanxi held out until 215. The generals who raised armies against them kept their troops. When the general-in-chief He Jin was assassinated on 22 September 189, officers stormed the palaces and killed about two thousand eunuchs. The warlord Dong Zhuo seized the boy emperor, burned Luoyang to the ground and moved the court to Chang’an in 191. In 196 Cao Cao brought Emperor Xian to Xuchang, and in 220 his son Cao Pi, king of Wei, took the throne, ending the dynasty and opening the Three Kingdoms period.
The registers show how far the state had broken down. A census taken in 280 AD, after the Jin dynasty reunified the country, recorded 16,163,863 people in 2,459,840 households, against 56,486,856 people in 10,677,960 households in a Han-era count. Historians caution that these numbers reflect who the state could tax, not who was alive: refugees and tax evaders vanished from the books, and warfare alone does not explain the gap. Still, the Han state that had once registered nearly 58 million people from Dunhuang to the Red River could, by the end, no longer count them at all.