"Let us go forward as with other matters and other measures similar in aim and effect - let us go forward in malice to none and good will to all. Such plans offer far better prizes than taking away other people's provinces or lands or grinding them down in exploitation. The empires of the future are the empires of the mind."
--Winston Churchill, "The Gift of a Common Tongue," September 1943
One of the more interesting unsolved puzzles of world history is why the region of the world now known as "China" has spent most of the last millennium united under one political regime, while all other centers of civilization, be they in Europe, the Near East, or the great Indic river basins, passed their days divided. Some push the unity of "Inner China" (modern China sans Manchuria, Inner Mongolia, Tibet, Xinjiang, Qinghai, Gansu, and Yunnan) back even further than this, and speak of a single Chinese empire stretching back to the beginnings of antiquity. This is not warranted. While inner China was united under one political regime several times in the first millennium, it was just as often divided between many warring nations and claimants. Were world historians writing their tomes in the 4th century AD, they would conclude that China was a land just as prone to division as Europe. In the millennium that preceded the Sui Dynasty's conquest of Inner China, the Chinese world had spent more centuries divided than united.
Things did not stay this way. In 581 AD he Sui Dynasty brought all of inner China brought under one regime's control for the second time. Over the centuries this feat that would be repeated by the Tang, Song, Yuan, Ming, and Qing in turn. Western history has no parallels to this. There was only ever one Roman Empire. Once it fell, no caliphate has ever matched the glories of the Umayyads.
Explanations for China's peculiar path are many. Some of these theories are more popular than others. The most popular is that Chinese unity was a product of Chinese geography. I debunked that notion in one of the more popular posts on this website. Read that post here, if you are interested; I will not retread that argument in this post. Here I want to tackle another common explanation for Chinese unity: China persisted through the centuries, this theory goes, because the idea of China as a unified empire persisted through all that time as well.
|China during one its eras of disuion, the age of "Five Dynasties and Ten Kingdoms."|
Map by Ian Kiu via Wikimedia Commons
Though its proponents don't really put it in these terms, their essential argument is that the ideal of Chinese unity was a Schelling point for conquerors. Every Chinese warlord and mandarin had a mental map of what needed to be controlled to in order to claim the Mandate of Heaven for themselves. "All Under Heaven" is what they called these lands, though even in ancient times it was quite apparent that there was far more under heaven than any emperor could administer. But the idea that certain areas were the natural inheritance of empire stuck around, as did the belief of the people who lived in those areas that they were really part of the same system and culture, even if it was temporarily divided between many regimes.
Europe lacked such a Schelling point, and this is why we talk of Napoleon and Hitler conquering Europe instead of reunifying it. That distinction is not just a semantic game: people treat foreign invasions and civil wars differently, and nations oft fight with greater fury to defend their homeland from foreign conquerors than domestic rebels. By this logic, part of the reason the conquests of tyrants like Hitler and Napoleon were so ephemeral was the fact these tyrants were perceived as conquerors, not reunifiers. Historians who study the war-torn history of China's republican era often bring up this distinction. The battles waged between warlords and political parties of that era were simply of a different character than the battles fought in China's war with Japan a few years later. Wars fought to reunify China fall in a different category than wars fought by outsiders to conquer her. 
However, there was nothing objective about the Japanese forces that made the Chinese people and their leaders treat them differently than they treated the forces of a Chinese warlord--in many cases, the soldiers of a warlord were just as alien to the 'natives' they conquered as the Japanese were. The Chinese soldier of the early 20th century, like his Japanese counterparts, usually spoke a different language and followed different customs than the people he fought amongst, and found himself just as bewildered by the climate and diet of the lands he was sent to fight for. The distinction between Japanese-led invasion and Chinese-led reunification existed only in the minds of those who made it. It was an idea--or rather, an iteration of an idea that had existed in some form for a thousand years of Chinese history. In the end it was the idea that there is one China and that this one China ought to be one and indivisible that made it so.
Or at least that is how the argument goes.
The most sophisticated versions of this argument pay special attention to how important ideas and the texts that held them were to the structure of imperial Chinese society. Mark Edward Lewis's account is compelling:
The Han imperium had created a new type of elite that was tied to the state through its economic dependence on salary and an intellectual commitment—more or less sincere—to the literary culture sanctioned by the court. However, the insecurity of office which the state used to assure the obedience of the officials meant that they were obliged to protect their futures, and those of their children, by finding resources outside the state sphere. Having obtained these resources, they ceased to be creatures of the state and became semi-independent local powers in the image of the great clans destroyed by Emperor Wu.
This became the classic form to the imperial Chinese elite, able to maintain itself only by balancing service to the state with the development of local bases. This type of elite was crucial to the conditioning of the state, which could never collect tax income sufficient to maintain a bureaucracy that was able to control the entire population. Instead the state maintained a bureaucracy that could preserve a degree of public order ad secure a sufficient income, and then relied on local powers to keep the peace where the state lacked the manpower to police The loyalty of these powers, in turn, was secured through the possibility of gaining crucial supplementary income through holding office or providing other services to the state.
In this system where the polity was created through the combination of paid agents and local allies, the texts of imperial canon served as the central cord binding the state proper to the powerful families on who it relied. Most families of the Eastern Han elite enriched themselves through office gained by study, or taken up study to secure wealth already gained. The canonical texts thus provided a major route by which families remained in states service. As the texts came to dominate the intellectual sphere, and serve the lingua franca of citations in which public debate was conducted, they also defined an intellectual frame in which state and families united in a common vision of society. The canonical texts instituted as a means of recruiting and controlling officials, thus became the core of a political system in which officials and dynasties were equally bound, and on which both depended. I do not disagree with Lewis' description. He has rather impressively distilled the entire imperial system into three paragraphs, and this stylized description of traditional China's political economy and social structure is probably the best I have seen. His account parallels historical sociologist Jack Goldstone's suggestion that we understand the traditional political and intellectual structures of Old War civilizations as "complex systems... [that had] the property of stable equilibria. even when greatly disturbed, they had self-restoring features, such as an elite committed to a core culture, key sacred defining texts that maintained their role at the center of that culture, and principles of rule including hereditary leadership, elite privileges and religious support for both."  Those looking to paint the inner workings of the early Islamic system, or its counterparts in Christendom, could do worse than take Lewis' three paragraphs as their guide.
However, it is knowledge of the history of these other civilizations that makes me question Lewis' final conclusion:
When the state defined itself through a group of texts, and justified itself through their teachings, then these writings could be invoked to criticize specific policies, or ultimately to condemn the state itself. These texts, however, also provided the means by which the imperial order could survive the demise of each of its incarnations. To the extent that this order was implanted in the values and aspirations of the powerful families, and that it was crucial both to their economic survival and their claims to superiority over rivals with no traditions of imperial service, the dream of empire would be carried forward and a new dynasty established in the rubble of the old. Thus writing was not only crucial to the administrative functioning of the state, but more important it served as the seed which, planted in the soil of local society, produced a new state each time the old one fell. Had we no knowledge of the other civilizations outside of China, this narrative would be a convincing one. We do have such knowledge, however, and it puts this theory into doubt. Simply stated, the ideology of imperial unity is not a Chinese invention. The Roman political system was just as dependent on an ideology that "dominated the intellectual sphere, and serve the lingua franca of citations in which public debate was conducted, they also defined an intellectual frame in which state and families united in a common vision of society" as the Chinese one was. This intellectual frame did not die with the Western Empire. It continued to dominate European politics and society for hundreds of years after Rome's collapse. Remember, the last man to claim the title Holy Roman Emperor died in 1835! The political and intellectual system of the Early Islamic empires has cast just as long a historical shadow. Men are killing and dying in the name of a resurrected Caliphate as you read this.
The problem was not that men and women in Mediterranean world stopped believing in the ideal of universal empire, nor even that elites stopped identifying with a broader imperial identity. The real problem was that those who inherited the intellectual legacy of Catholic Empire and Universal Caliphate did not also inherit the administrative tools needed to administer one. The Dark Ages was a time where men could dream of empire but could not build one. In Europe the decisive moment came piecemeal to different parts of the continent, first as the Carolingian empire collapsed, then when the Caliphate of Cordoba followed in its footsteps, and finally after the Investiture conflict and the civil war that followed left the Salians in only nominal control of their realm. Power was so forcefully decentralized in the decades that followed each collapse that some historians argue we should not describe the feudal structures that followed as "governments" at all.  Europeans of this era did not forget how to dream, but they had forgotten how to govern. It would take centuries of state building until Europeans had regained the ability to field armies, administer taxes, and incorporate new conquests into their kingdoms. The slate was wiped clean clean. By these new states became strong enough to extend their control over distant lands, the memory of Rome ha dimmed and identity had reverted to the centers of local power where state building had begun. 
This process never happened in China. The Chinese also continued to dream of unity--but more importantly, they never completely lost their capacity to transform their dreams into reality. The imperial center was destroyed, but the bureaucratic structures that held the imperial system together at the lower levels of society lived on. The structures used to govern China and wring taxes from the Chinese people did change over the course of Chinese history, but there was never anything comparable to the total administrative collapse seen in early medieval Europe or the late medieval Near East .The old regime had been decentralized, but not destroyed. This not just made it easier for the next generation of Chinese warlords to mobilize the armies needed to reconquer all of China, but it also made it far easier for them to incorporate what they conquered as fiscally productive parts of their domain.
Each period of unification deepened the connections between different regions of China, making it that much easier for warlords, rebels, and foreign conquerors to administer their new conquests then next time China fell apart. It's a classic example of virtuous cycle at work. The more time China spent unified the easier it was to unify it in the future. This led to one of the more striking patterns of Chinese history: each major period of disunity was shorter than the last.
The logic of Schelling points and the ideals of universal empire played a part in all this, and of course the longer China was unified the stronger these ideals would be. However, as the Western experience suggests, imperial ideology may have been a necessary condition of unification, but it was not a sufficient one. Ideas alone do not make empires. China was never an empire of the mind. Like all else built by the hands of man, China was a creation of blood, toil, and fear.
 Mark Edward Lewis, Writing and Authority in Ancient China (Albany: State University of New York Press, 1999), 361.
 Jack Goldstone, "The Origins of Western Superiority: A comment on Modes of Meta-History and Duchesne’s Indo-Europeans," Cliodynamics 4, no 1 (2013), 63.
 Lewis, Writing and Authority, 361.
 Thomas Bison, The Crisis of the Thirteenth Century: Power, Lordship, and the Origins of
European Government (Princeton: Princeton University Press, 2009), 1-22.
 The literature on European state building in the medieval and pre-modern eras is vast. Charles Tllly's Coercion, Capital, and European States is the classic account, though this gloss--particular the details regarding the onset of systematic collapse--is indebted to Thomas Ertman's Birth of the Leviathan: Building States and Regimes in Early Modern Europe.
Readers may also be interested in seeing my white paper comparing the state building experiences of early modern Europe, ancient China, and medieval Japan for a more thorough review of the literature.