Introduction

"So Peace Brings Warre and Warre Brings Peace"

The empire has unified all the civilizations at last. After generations of battles, the last enemies have been defeated. Citizens of the empire can, it seems, look forward to permanent peace and prosperity. But a maverick mathematician named Hari Seldon has disturbing news. His new science of psychohistory, built from equations that integrate the actions of myriads of individuals, predicts large-scale social trends. When the equations are run forward, they foretell the decay and eventual collapse of the central power, rebellions by regional barons and rogue generals, and finally a bitter civil war that will transform the capital of the empire from a teeming metropolis of hundreds of billions into a ghost town with a few thousand survivors eking out a miserable living among the ruins. The decline and fall of the empire over the ensuing centuries unfolds precisely as the humble mathematician said it would.

This scenario from the Foundation trilogy of Isaac Asimov occurs in the future on the planet Trantor, the capital of a mighty galactic empire. In Asimov's fantasy, human history can be understood and predicted in the same way that physicists understand and predict the trajectories of planets, or biologists the expression of the gene. The key to the prediction of human societies is psychohistory, the "branch of mathematics which deals with the reactions of human conglomerates to fixed social and economic stimuli." The ability of psychohistorians to make accurate forecasts, however, is not absolute. Psychohistory cannot accurately predict actions of a single individual. Furthermore, the knowledge of the prediction must be withheld from the people whose collective behavior is predicted. As Hari Seldon explains, "By knowledge, your freedom of action would be expanded and the number of additional variables introduced would become greater than our psychology could handle." Prediction of human societies might also prove impossible for another reason: Complex dynamic systems are inherently unpredictable in the long run because of "the butterfly effect." Small causes might produce large effects. For example, a butterfly fluttering its wings in Australia might cause a hurricane in the Atlantic. Or, as a children's rhyme has it, "For want of a nail... the kingdom was lost." Asimov, however, could not know about the butterfly effect because he wrote the trilogy in the early 1950s, before the discovery of mathematical chaos.

Asimov's trilogy captured the imagination of millions of readers, among them quite a few scientists and historians. However, his vision flies in the face of the view held by most professional historians and scientists, a view generally accepted in our culture. For centuries, philosophers have mulled over the prospects of a scientific study of history. Despite some dissenting voices, the consensus has been that scientific study of human societies is impossible because they differ too much from physical and biological systems. They are too complex. They consist not of simple identical particles, such as atoms and molecules, but of human individuals, each unique, endowed with free will, and capable of purposeful action. The verdict has been that any sort of scientific history must remain science fiction rather than a real science. And some might believe that this is for the best.

A science of history sounds cold and hard—wouldn't it destroy our enjoyment of the wonderfully rich tapestry of the past? On a darker side, might not such a science enable some shadowy cabal to manipulate societies to a nefarious purpose? But have we ceased to enjoy the blue sky of a brilliant summer day, or the play of colors in a glorious sunset? After all, the physicists, beginning with Newton and ending with Einstein, worked out exactly how colors of the sky result from the interaction of sunlight with the atmosphere. As to the nefarious uses of a science of history, it is true that any knowledge can be turned to good or bad ends. But Asimov's notion of a Second Foundation—a group of psychohistorians pulling the strings from some secret center—was always the least credible part of his vision.

War and Peace and War addresses the question raised by Asimov (and many other people before him, including Marx and Tolstoy): Is a science of history possible? Can we design a theory for the collapse of mighty empires that would be no worse than, say, our understanding of why earthquakes happen? Seismologists have made great strides in understanding earthquakes. They can even make some limited predictions as to which areas of the earth are likely to be hit next by an earthquake. However, forecasting the precise timing and magnitude of an earthquake eludes them. Can a science of history, similarly, explain why states crumble, and perhaps predict which societies are in the danger of collapse?

This book focuses on empires. Why did some—initially small and insignificant—nations go on to build mighty empires, whereas other nations failed to do so? And why do the successful empire builders invariably, given enough time, lose their empires? Can we understand how imperial powers rise and why they fall?

An empire is a large, multiethnic territorial state with a complex power structure. The key variable is the size. When large enough, states invariably encompass ethnically diverse people; this makes them into multiethnic states. And given the difficulties of communication in pre-industrial times, large states had to come up with a variety of ad hoc ways to bind far-flung territories to the center. One of the typical expedients was to incorporate smaller neighbors as self-contained units, imposing tribute on them and taking over their foreign relations, but otherwise leaving their internal functioning alone. Such a process of piecemeal accumulation usually leads to complicated chains of command and the coexistence of heterogeneous territories within one state.

Empires are not the only objects of study for a science of history. Historians such as Arnold Toynbee wrote volumes on the rise and fall of whole civilizations. Others have been fascinated with the spread of world religions, evolution of art styles, progress in science and technology, or economic and demographic changes. All of these subjects are worthy. However, it is impossible to encompass them all in one book. The rise and fall of empires is a fine place to start.

Unlike such entities as civilizations, territorial states are easier to define and demarcate from each other, as well as from other comparable units (city states, tribal confederations, and so on). Historians continue to argue about how to distinguish one civilization from another. Different authorities place Achaemenid Persia as part of the Syriac, Iranian, or Mesopotamian civilization. In contrast to this multitude of contending notions, were you to consult any historical atlas, you would find the boundaries of the Achaemenid Empire drawn in pretty much the same places.

Although the doings of empires dominate the historical records, we should not conclude that they are the norm in human history. Prior to the nineteenth century most (and until six thousand years ago all) of the habitable space on Earth was divided among small-scale, stateless societies, not empires. Historical empires themselves, as often as not, were in the state of decline or even disintegration. A large stable empire, internally at peace, is a rarity in history. Looked at from this point of view, the most fundamental question requiring an explanation is not why empires decline and collapse, but how they manage to get going in the first place. How are empires possible?

The stories of empire are irresistible. Imagine the feelings of an eighteenth-century Englishman, on his world tour, standing among the fairly well-preserved 2,000-year-old ruins of ancient Rome (before the modern metropolis engulfed them). Today one can have a similar experience in Chichen Itza in Mexico. (Be sure to get there early in the day before the tourist buses arrive.) Who were the people who built these magnificent temples and pyramids? Why aren't they around anymore? From Shelley's "Ozymandias" to Darth Vader, stories of empires fascinate us.

As a road map to what follows, here is a very terse outline of the central theoretical argument of the book.

Many historical processes are dynamic—empires rise and fall, populations and economies boom and bust, world religions spread or wither. The field of historical dynamics investigates such dynamic processes in history. Most research has been done on agrarian societies, those in which the majority (and often more than 90 percent) of people are involved in producing food.

The theoretical framework I have been developing for several years focuses not on human individuals, but on social groups through time. Ultimately, the behavior of a group is determined by the actions of its individual members. However, social groups are not simple collections of identical particles, readily described by statistical physics; they have complex internal structures.

One important aspect of group structure is that different people have access to differing amounts of power and wealth. A small number of members of an agrarian society (typically around 1 or 2 percent) concentrates in its hands most of the power and wealth; this group consists of the elites or aristocracy. Commoners make up the rest of the population.

Another important aspect of social structure is ethnicity. Ethnicity is the group use of any aspect of culture to create internal cohesion and differentiation from other groups. An imaginary boundary separates the members of the ethnic group from the rest of humanity. For example, Greeks drew a boundary between themselves and barbarians, non-Greek speakers. The ethnic boundary can use a variety of symbolic m...