Empires rise, and then, with some apparent regularity, they fall, and in doing so, they provide historians with one of their most intriguing questions: what causes the collapse of these once-mighty structures? In China, the Han dynasty empire came to an end in 220 C.E.; the traditional date for the final disintegration of the Roman Empire is 476 C.E., although a process of decline had been under way for several centuries. In the Roman case, however, only the western half of the empire collapsed, while the eastern part, subsequently known as the Byzantine Empire, maintained the tradition of imperial Rome for another thousand years.

Despite these differences, a number of common factors have been associated with the end of these imperial states. At one level, they both simply got too big, too overextended, and too expensive to be sustained by the available resources, and no fundamental technological breakthrough was available to enlarge these resources. Furthermore, the growth of large landowning families with huge estates and political clout enabled them to avoid paying taxes, turned free peasants into impoverished tenant farmers, and diminished the authority of the central government. In China, such conditions led to a major peasant revolt, known as the Yellow Turban Rebellion, in 184 C.E. (see Chapter 5).

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Rivalry among elite factions created instability in both empires and eroded imperial authority. In China, persistent tension between castrated court officials (eunuchs) loyal to the emperor and Confucian-educated scholar-bureaucrats weakened the state. In the Roman Empire between 235 and 284 C.E., some twenty-six individuals claimed the title of Roman emperor, only one of whom died of natural causes. In addition, epidemic disease ravaged both societies, though more extensively in the Roman world. The population of the Roman Empire declined by 25 percent in the two centuries following 250 C.E., a demographic disaster that meant diminished production, less revenue for the state, and fewer men available for the defense of the empire’s long frontiers.

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Historians have often linked the collapse of empires with environmental factors as well, more often with reference to Rome than to Han dynasty China. Considerable fluctuations in the climate after about 250 C.E. led to drought in the third century, cold and wet conditions in the fourth, and increased rainfall and cooler temperatures in the fifth, all of which generated substantial soil erosion and declining agricultural productivity. The North African breadbasket of the empire suffered from serious salinization and increasingly desert-like conditions. The extent to which such factors contributed to the collapse of the Roman Empire remains a point of dispute among scholars.

To these mounting internal problems was added a growing threat from nomadic or semi-agricultural peoples occupying the frontier regions of both empires. The Chinese had long developed various ways of dealing with the Xiongnu and other nomadic people to the north — building the Great Wall to keep them out, offering them trading opportunities at border markets, buying them off with lavish gifts, contracting marriage alliances with nomadic leaders, and conducting periodic military campaigns against them. But as the Han dynasty weakened in the second and third centuries C.E., such peoples more easily breached the frontier defenses and set up a succession of “barbarian states” in north China. Culturally, however, many of these foreign rulers gradually became Chinese, encouraging intermarriage, adopting Chinese dress, and setting up their courts in Chinese fashion.

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A weakening Roman Empire likewise faced serious problems from Germanic-speaking peoples living on its northern frontier. Growing numbers of these people began to enter the empire in the fourth century C.E.— some as mercenaries in Roman armies and others as refugees fleeing the invasions of the ferocious Huns, who were penetrating Europe from Central Asia. Once inside the declining empire, various Germanic groups established their own kingdoms, at first controlling Roman emperors and then displacing them altogether by 476 C.E. Unlike the nomadic groups in China, who largely assimilated Chinese culture, Germanic kingdoms in Europe developed their own ethnic identities — Visigoths, Franks, Anglo-Saxons, and others — even as they drew on Roman law and adopted Roman Christianity. Far more than in China, the fall of the western Roman Empire produced a new culture, blending Latin and Germanic elements, which provided the foundation for the hybrid civilization that would arise in Western Europe.

The collapse of empire meant more than the disappearance of centralized government and endemic conflict. In post-Han China and post-Roman Europe, it also meant the decline of urban life, a contracting population, less area under cultivation, diminishing international trade, and vast insecurity for ordinary people. It must have seemed that civilization itself was unraveling.

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The most significant difference between the collapse of empire in China and that in the western Roman Empire lay in what happened next. In China, after about 350 years of disunion, disorder, frequent warfare, and political chaos, a Chinese imperial state, similar to that of the Han dynasty, was reassembled under the Sui (589–618 C.E.), Tang (618–907), and Song (960–1279) dynasties. Once again, a single emperor ruled; a bureaucracy selected by examinations governed; and the ideas of Confucius informed the political system. Such a Chinese empire persisted into the early twentieth century, establishing one of the most continuous political traditions of any civilization in world history.

The story line of European history following the end of the western Roman Empire was very different indeed. No large-scale, centralized, imperial authority encompassing all of Western Europe has ever been successfully reestablished there for any length of time. The memory of Roman imperial unity certainly persisted, and many subsequently tried unsuccessfully to re-create it. But most of Western Europe dissolved into highly decentralized political systems involving nobles, knights and vassals, kings with little authority, various city-states in Italy, and small territories ruled by princes, bishops, or the pope. From this point on, Europe would be a civilization without an encompassing imperial state.

From a Chinese point of view, Western Europe’s post-Roman history must seem an enormous failure. Why were Europeans unable to reconstruct something of the unity of their classical empire, while the Chinese clearly did? Surely the greater cultural homogeneity of Chinese civilization made that task easier than it was amid the vast ethnic and linguistic diversity of Europe. The absence in the Roman legacy of a strong bureaucratic tradition also contributed to European difficulties, whereas in China the bureaucracy provided some stability even as dynasties came and went. The Chinese also had in Confucianism a largely secular ideology that placed great value on political matters in the here and now. The Roman Catholic Church in Europe, however, was frequently at odds with state authorities, and its “otherworldliness” did little to support the creation of large-scale empires. Finally, Chinese agriculture was much more productive than that of Europe, and for a long time its metallurgy was more advanced.16 These conditions gave Chinese state builders more resources to work with than were available to their European counterparts.