Founded by the peasant-born military leader Liu Bang in 206 BCE following the collapse of the brutal Qin dynasty, the Han dynasty ruled China for over four centuries (206 BCE–220 CE) and is considered the first golden age of Chinese civilization. Under Emperor Wu (r. 141–87 BCE), Han armies expelled the Xiongnu nomads from Central Asia and secured the trade corridors that became the Silk Road, connecting China to Persia, India, and Rome. Paper was invented during the Han period by the court official Cai Lun. Confucianism was adopted as the official state ideology, and the civil service examination system was established — selecting government officials based on merit rather than birth for the first time in history. The Han population reached 58 million, and the capital Chang'an (modern Xi'an) rivaled Rome as one of the world's largest cities. The dynasty's cultural legacy is so foundational that the majority ethnic group in China, the Chinese language, the Chinese script, and traditional Chinese dress are all still called "Han." The brief interruption of Wang Mang's usurpation (9–23 CE) divides the dynasty into the Western Han and Eastern Han periods. The Han dynasty collapsed in 220 CE due to court intrigue, peasant rebellion, and regional warlordism, fragmenting China into the Three Kingdoms.