Much of what came to constitute China Proper was unified for the first time in 221 B.C. In that year the western frontier state of Qin, the most aggressive of the Warring States, subjugated the last of its rival states. (Qin in Wade-Giles romanization is Ch'in, from which the English China probably derived.) Once the king of Qin consolidated his power, he took the title Shi Huangdi ( First Emperor), a formulation previously reserved for deities and the mythological sage-emperors, and imposed Qin's centralized, nonhereditary bureaucratic system on his new empire. In subjugating the six other major states of Eastern Zhou, the Qin kings had relied heavily on Legalist scholar-advisers. Centralization, achieved by ruthless methods, was focused on standardizing legal codes and bureaucratic procedures, the forms of writing and coinage, and the pattern of thought and scholarship. To silence criticism of imperial rule, the kings banished or put to death many dissenting Confucian scholars and confiscated and burned their books (). Qin aggrandizement was aided by frequent military expeditions pushing forward the frontiers in the north and south. To fend off barbarian intrusion, the fortification walls built by the various warring states were connected to make a 5,000-kilometer-long great wall (). What is commonly referred to as the Great Wall is actually four great walls rebuilt or extended during the Western Han, Sui, Jin, and Ming periods, rather than a single, continuous wall. At its extremities, the Great Wall reaches from northeastern Heilongjiang () Province to northwestern Gansu (). A number of public works projects were also undertaken to consolidate and strengthen imperial rule. These activities required enormous levies of manpower and resources, not to mention repressive measures. Revolts broke out as soon as the first Qin emperor died in 210 B.C. His dynasty was extinguished less than twenty years after its triumph. The imperial system initiated during the Qin dynasty, however, set a pattern that was developed over the next two millennia.

After a short civil war, a new dynasty, called Han (206 B.C.-A.D. 220), emerged with its capital at Chang'an ( ). The new empire retained much of the Qin administrative structure but retreated a bit from centralized rule by establishing vassal principalities in some areas for the sake of political convenience. The Han rulers modified some of the harsher aspects of the previous dynasty; Confucian ideals of government, out of favor during the Qin period, were adopted as the creed of the Han empire, and Confucian scholars gained prominent status as the core of the civil service. A civil service examination system also was initiated. Intellectual, literary, and artistic endeavors revived and flourished. The Han period produced China's most famous historian, Sima Qian ( 145-87 B.C.?), whose Shiji ( Historical Records) provides a detailed chronicle from the time of a legendary Xia emperor to that of the Han emperor Wu Di ( 141-87 B.C.). Technological advances also marked this period. Two of the great Chinese inventions, paper and porcelain, date from Han times.

The Han dynasty, after which the members of the ethnic majority in China, the "people of Han," are named, was notable also for its military prowess. The empire expanded westward as far as the rim of the Tarim Basin (in modern Xinjiang-Uyghur Autonomous Region), making possible relatively secure caravan traffic across Central Asia to Antioch, Baghdad, and Alexandria. The paths of caravan traffic are often called the "silk route" () because the route was used to export Chinese silk to the Roman Empire. Chinese armies also invaded and annexed parts of northern Vietnam and northern Korea toward the end of the second century B.C. Han 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.

After 200 years, Han rule was interrupted briefly (in A.D. 9-24 by Wang Mang or , a reformer), and then restored for another 200 years. The Han rulers, however, were unable to adjust to what centralization had wrought: a growing population, increasing wealth and resultant financial difficulties and rivalries, and ever-more complex political institutions. Riddled with the corruption characteristic of the dynastic cycle, by A.D. 220 the Han empire collapsed.

Era of Disunity

The collapse of the Han dynasty was followed by nearly four centuries of rule by warlords. The age of civil wars and disunity began with the era of the Three Kingdoms (Wei, Shu, and Wu, which had overlapping reigns during the period A.D. 220-80). In later times, fiction and drama greatly romanticized the reputed chivalry of this period. Unity was restored briefly in the early years of the Jin dynasty (A.D. 265-420), but the Jin could not long contain the invasions of the nomadic peoples. In A.D. 317 the Jin court was forced to flee from Luoyang and reestablished

itself at Nanjing to the south. The transfer of the capital coincided with China's political fragmentation into a succession of dynasties that was to last from A.D. 304 to 589. During this period the process of sinicization accelerated among the non-Chinese arrivals in the north and among the aboriginal tribesmen in the south. This process was also accompanied by the increasing popularity of Buddhism (introduced into China in the first century A.D.) in both north and south China. Despite the political disunity of the times, there were notable technological advances. The invention of gunpowder (at that time for use only in fireworks) and the wheelbarrow is believed to date from the sixth or seventh century. Advances in medicine, astronomy, and cartography are also noted by historians.