The rapidity of change in modern societies is among the most distinctive features of recent history, but change and transformation, though at various rates, have been constants in the human story since the very beginning. Explaining how and why human societies change is perhaps the central issue that historians confront, no matter which societies or periods of time they study. Those who specialize in the history of some particular culture or civilization often emphasize sources of change operating within those societies, although there is intense disagreement as to which are most significant. The ideas of great thinkers, the policies of leaders, struggles for power, the conflict of classes, the invention of new technologies, the growth or decline in population, variations in climate or weather—all of these and more have their advocates as the primary motor of historical transformation.

Of course, it is not necessary to choose among them. The history of China illustrates the range of internal factors that have driven change in that civilization. The political conflicts of the “era of warring states” provided the setting and the motivation for the emergence of Confucianism and Daoism, which in turn have certainly shaped the character and texture of Chinese civilization over many centuries. The personal qualities and brutal policies of Shihuangdi surely played a role in China’s unification and in the brief duration of the Qin dynasty. The subsequent creation of a widespread network of canals and waterways as well as the country’s technological achievements served to maintain that unity over very long periods of time. But the massive inequalities of Chinese society generated the peasant upheavals, which periodically shattered that unity and led to new ruling dynasties. Sometimes natural events, such as droughts and floods, triggered those rebellions.

World historians, more than those who study particular civilizations or nations, have been inclined to find the primary source of change in contact with strangers, in external connections and interactions, whether direct or indirect. The history of China and East Asia provides plenty of examples for this point of view as well. Conceptions of China as the “middle kingdom,” infinitely superior to all surrounding societies, grew out of centuries of involvement with its neighbors. Some of those neighbors became Chinese as China’s imperial reach grew, especially to the south. Even those that did not, such as Korea, Vietnam, and Japan, were decisively transformed by proximity to the “radiating civilization” of China. China’s own cuisine, so distinctive in recent centuries, may well be a quite recent invention, drawing heavily on Indian and Southeast Asian cooking. Buddhism, of course, is an obvious borrowing from abroad, although its incorporation into Chinese civilization and its ups and downs within China owed much to internal cultural and political realities.

In the end, clear distinctions between internal and external sources of change in China’s history—or that of any other society—are perhaps misleading. The boundary between “inside” and “outside” is itself a constantly changing line. Should the borderlands of northern China, where Chinese and Turkic peoples met and mingled, be regarded as internal or external to China itself? And, as the histories of Chinese Buddhism and of Japanese culture so clearly indicate, what comes from beyond is always transformed by what it encounters within.