The Han Dynasty; 206 BC–220 AD) followed the Qin Dynasty and preceded the Three Kingdoms in China. The Han Dynasty was ruled by the prominent family known as the Liu clan. The reign of the Han Dynasty, lasting over 400 years, is commonly considered within China to be one of the greatest periods in the history of China. To this day, the ethnic majority of China still refer to themselves as the "Han people." During the Han Dynasty, China officially became a Confucian state and prospered domestically: agriculture, handicrafts and commerce flourished, and the population reached over 55 million people. Meanwhile, the empire extended its political and cultural influence over Korea, Mongolia, Vietnam, Japan, and Central Asia before it finally collapsed under a combination of domestic and external pressures. The first of the two periods of the dynasty was the Former Han Dynasty or Western Han Dynasty 206 BC–24 AD, seated at Chang'an. The Later Han Dynasty or Eastern Han Dynasty 25–220 AD was seated at Luoyang. The western-eastern Han convention is currently used to avoid confusion with the Later Han Dynasty of the Period of the Five Dynasties and the Ten Kingdoms although the former-later nomenclature was used in history texts including Sima Guang's Zizhi Tongjian. The Han Dynasty was notable also for its military prowess. The empire expanded westward to the Tarim Basin (in modern Xinjiang-Uyghur Autonomous Region), with military expeditions as far west as beyond the Caspian Sea, making possible a relatively safe and secure caravan and merchantile traffic across Central Asia. The paths of caravan traffic came to be known as the "Silk Road" because the route was used to export Chinese silk. Chinese armies also invaded and annexed parts of northern Korea (Wiman Joseon) and northern Vietnam toward the end of the 2nd century BC. Han Dynasty control of peripheral regions was generally insecure, however. To ensure peace with non-Chinese local powers, the Han court developed a mutually beneficial "tributary system." Non-Chinese states were allowed to remain autonomous in exchange for symbolic acceptance of Han overlordship. Tributary ties were confirmed and strengthened through intermarriages at the ruling level and periodic exchanges of gifts and goods.