War: What is it good for?

by Ian Morris

  India’s experience revealed the hard fact that revolutions in military affairs are irresistible. As dominoes fell and agrarian empires came under pressure, the empires could either turn themselves into cavalry powers, as Persia and China did, or, like India, be overrun by nomad groups that were already cavalry powers—in which case the invaders would turn the society they conquered into a cavalry power anyway. The choices rulers made might speed up or slow down the process, but the paradoxical logic of war always won in the end.

  In the same years, the Han Empire in China (which had started India’s woes by setting dominoes tumbling across the steppes) learned an even harder fact—that the long story of the empires’ entanglement with the steppes was now reaching its culminating point. China had been fighting Xiongnu nomads along its northern frontier since 200 B.C., but all had been quiet on its western front, which was shielded from the steppes by a hundred-mile-thick band of mountains and forests. But that changed when the Xiongnu migrated around 50 B.C. While one branch of the confederation moved west and toppled the dominoes that drove the Yuezhi and Shakas into India, a second branch moved south, plundering the Qiang farmers on China’s western border.

  For decades, the Qiang had shielded China by fighting bitter frontier wars against hit-and-run nomad raids, but in the first century A.D., caged between the nomads and the Han imperial frontier, the Qiang began to form their own governments. Large, well-organized groups of Qiang moved into Han territory to get away from the Xiongnu, fighting the empire’s troops if they had to. The Qiang were changing from a shield into a sword, thrusting at the empire’s vitals.

  Chinese border officials could see where things were heading. “Recently,” one observed in 33 B.C., “the Western Qiang have guarded our frontier, and thus come into regular contact with Han people”; however, his report continues, as more Qiang moved into Han territory, “minor officials and greedy commoners have robbed the Qiang of cattle, women, and children. This has provoked the Qiang’s hatred, so they have risen in rebellion.”

  In the first century A.D., the Han lost control of their western frontier. In A.D. 94, 108, and again in 110, great rebellions/invasions (it was hard to tell the two apart) got out of hand. The borderlands spiraled down into violence. “Even women bear halberds and wield spears, clasp bows in their hands and carry arrows on their backs,” an official named Gong Ye lamented.

  At the far western end of Eurasia, a similar set of facts was about to end Agricola’s productive war and bring Rome to the same culminating point. The Roman Empire had long been shielded from the steppes by a zone of Germanic herders and farmers that was even thicker than the Qiang zone on China’s western frontier, but here, too, steppe migrations now turned the shield into a sword aimed at the empire’s heart.

  The motor might have been the Sarmatians, nomads living along the Don River, who began moving west in the first century A.D. They were a fierce lot: according to Herodotus, they descended from the Amazons, and no Sarmatian woman was allowed to marry until she had killed a man in battle. Be that as it may, their distinctive combination of light and heavy cavalry, with horse archers disrupting enemy lines before armored riders charged home with spears, proved devastating. It was the arrival of a Sarmatian tribe called the Iazyges on the north bank of the Danube in the early 80s A.D. that prompted Domitian to recall Agricola’s troops from Britain, and the spread of other tribes across eastern Europe caused chaos for everyone whose path they crossed.

  In the first two centuries A.D., warmer weather brought population growth to Europe, increasing caging among German farmers. Consequently, any tribe that tried to get out of the Sarmatians’ way immediately set off desperate wars with neighbors determined to defend their fields. The Germans living nearest the steppes copied their tormentors and started fighting from horseback, and even those Germans farthest from the steppes adopted better weapons and tactics. Under the pressure of war, chiefs turned into kings who centralized power, extracted taxes, and organized real armies.

  Sometime around A.D. 150, a German people known as the Goths abandoned their old farmlands near the Baltic Sea and began drifting south, toward the Black Sea. Their great trek drove other tribes before them, until in the 160s a vast federation, called Marcomanni (literally, “Border Folk”) by the Romans, started pushing across the Danube. Germans had been drifting back and forth across Rome’s frontiers for centuries, usually coming as small bands of young men looking for work or stealing what they could, then running home again, but this time was different. Now thousands of families were on the move and planning to stay.

  Confronting them was Marcus Aurelius (Figure 3.4), Rome’s emperor between A.D. 161 and 180. More than anyone else, it was this learned, literate, and humane man—perhaps the ultimate stationary bandit—whom Gibbon had in mind when he called the second century A.D. the happiest age of mankind. Given the choice, Marcus would have spent his days disputing the finer points of Stoic philosophy with bearded Greek professors, but the storms on the steppes instead forced him to spend them fighting and marching through the forests beyond the Danube. By going without sleep in the breaks from battle, he did, however, find time to write the Meditations, the classic of Stoic thought. (If any ancient emperor deserves the label “great man,” it is surely Marcus.)

  Figure 3.4. Warrior for the working day: bronze equestrian statue of Marcus Aurelius (Roman emperor, A.D. 161–180)

  Like Eisenhower’s successors in the 1960s, Marcus was pulled by the need to prop up dominoes into a war he never wanted, fought in ways he never anticipated. Harry Summers, an American army colonel, tells a story about being sent on a delegation to Hanoi in 1975, soon after Eisenhower’s prediction had come true and the South Vietnamese domino had fallen. An English-speaking North Vietnamese officer named Colonel Tu met him at the airport, and, not surprisingly, their conversation soon drifted toward the late unpleasantness between their countries.

  “You know,” Summers told Tu, “you never defeated us in the field.”

  Tu thought for a moment. “That may be true,” he finally said. “But it is also irrelevant.”

  Like the Americans in Vietnam, Roman armies in the 160s A.D. could usually count on beating their enemies in a straight fight,1 and like the North Vietnamese the Germans therefore sought to make such fights irrelevant. As a result, Rome’s proud legions were reduced to tactics all too familiar from Vietnam. With alarming honesty, the column set up to adorn Marcus Aurelius’s tomb in 180 was decorated as much with scenes of Romans burning villages, stealing farm animals, and killing prisoners as with fights between armed men (Figure 3.5).

  Figure 3.5. Destroying the village to save it: Roman troops burn huts and drag away women and children on a monument erected in Marcus Aurelius’s honor in the 180s A.D.

  To make things worse, when the Romans did get pitched battles, they were rarely the kind they expected. The first time Roman troops ran into the Iazyges’ cavalry, for instance, they got an unpleasant shock. Using classic nomad tactics, the Iazyges pretended to run away, luring a legion out onto the frozen Danube. With their pursuers slithering around on the ice, the riders doubled back, surrounded the Romans, and came in for the kill.

  Only the Romans’ discipline saved them. “The Romans stayed calm,” the historian Cassius Dio wrote.

  They formed a square, facing all the attackers. Most of the men put their shields down and stood with one foot on them, so they wouldn’t slip as much. Then they took the enemy’s charge. They grabbed the riders’ bridles, shields, and spears. Pulling them forward, they dragged men and horses over. If a Roman fell backwards, he pulled his enemy on top of him, then used his legs to flip him over, like a wrestler, and got on top. If he fell forward, he would bite the Sarmatian … The barbarians, not used to this kind of thing, and wearing lighter armor, lost heart. Only a few escaped.

  On that day, Rome’s infantry beat the cavalry, but over the next hundred years more and more Germans took to horseback, and more and more Sarmatians (and other nomads
) raided as far as the borders. Compounding Rome’s misery, an assertive new dynasty—the Sasanids—seized the Persian throne in A.D. 224 and began fielding thousands of cataphracts, superheavy cavalry with horses as well as riders encased in chain mail and steel. “All the companies were clad in metal,” a Roman eyewitness wrote in the fourth century, “so well fitted that the stiff joints conformed with those of the riders’ limbs. Images of faces were so skillfully fitted to their helmets that their bodies were completely armored. The only spots where arrows could lodge were the little holes left for their eyes and nostrils, which allowed them a little light and air.”

  Historians argue fiercely over exactly when the Romans drew the obvious conclusion that they needed more cavalry of their own, but between about A.D. 200 and 400 Rome moved down the same road as Persia, China, and India. The proportion of horsemen in Roman armies rose from about one in ten to one in three or even one in two, and by A.D. 500 the latest revolution in military affairs was complete. From the Mediterranean to the Yellow Sea, the war horse reigned supreme.

  Just how each empire used cavalry varied with geography. The Han and Kushans relied on hosts of light horsemen, striking quickly across the open steppes; the Sasanid Persians, on frontal charges by armored knights with spears; and the Romans, on combined-arms tactics, raiding deep into barbarian forests to burn villages and ambush troublemakers. But each system worked well enough against its immediate enemies, and for the first few centuries A.D. it was rarely obvious that the ancient empires had horribly overshot the culminating point of their productive wars.

  It took an altogether unanticipated enemy to bring that point home.

  The Graveyard of Empires

  Aristocrats in the ancient empires loathed nomads. For Herodotus, Scythian scalping practices said it all. “When a Scythian kills his first man, he drinks some of his blood, and brings the head back to the king,” he recorded. Next, “he cuts the head in a circle around the ears, and then, taking hold of it, shakes off the skin. Then he scrapes it out with an ox’s rib and works the skin in his hands till he has made it soft; and then he uses it as a napkin.” A thousand years later, the Roman writer Ammianus Marcellinus was even blunter about the Huns. “They have squat bodies, strong limbs, and thick necks,” he insisted, “and are so hideous and deformed that they might be two-legged beasts.”

  What should really have alarmed these civilized gentlemen, however, was not the nasty nomads who came riding in on horses. It was the even nastier microbes that came riding in on the nomads.

  Right up to the twentieth century A.D., the biggest killer in war was always disease. By bringing together thousands of men, packing them into small spaces, feeding them badly, and leaving them to wallow in their own filth, armies acted as petri dishes in which microbes could multiply madly. In crowded, unsanitary camps, exotic viruses thrived even when they killed their human hosts, because there was always another host to leap to. Dysentery, diarrhea, typhoid, and tuberculosis: these have ever been the soldier’s lot.

  But in A.D. 161, the year Marcus Aurelius assumed the purple in Rome, something even worse was brewing. We hear of it first on China’s northwest frontier, where, as so often, a large army was fighting the steppe nomads. Reports describe a puzzling new disease, which killed a third of the men in the camps within a few weeks. Four years later, equally awful infections raged through Roman military bases in Syria. The sickness reached the city of Rome in 167, where it killed so many people that Marcus delayed his departure for the Danube while he performed rites to protect the city. When his army did leave for the front, it took the disease with it.

  Descriptions by eyewitnesses make the plague sound a bit like smallpox. Geneticists have yet to confirm this from ancient DNA, but we can be fairly sure that the cause of the simultaneous outbreaks at each end of Eurasia was the tumbling of dominoes on the steppes. For thousands of years, each of the great Eurasian civilizations had been evolving its own unique disease pool. In perfect Red Queen style, lethal pathogens and protective antibodies raced against each other, running faster and faster but getting nowhere, staying neck and neck in an unhealthy equilibrium. Between one-quarter and one-third of all babies died within a year or so of being born; few adults survived past fifty; and even when people were in what passed for the best of health, their bodies oozed with germs.

  Distance had kept these disease pools separate, but the success of productive war changed that. As the empires grew, migrants moved between them, particularly across the steppes. Mobility merged the previously distinct disease pools, brewing up a vicious epidemiological cocktail that was new to everyone. Not many people were lucky enough to have been born with antibodies that could fight it, and until their robust genes spread through the pool of survivors (which could take centuries), the plagues kept coming back.

  The best records come from Egypt, where the population apparently fell by a quarter between A.D. 165 and 200. Elsewhere we are forced to guess from archaeological remains, but these suggest that Egypt’s experience was widely shared. With fewer people around, empires then struggled to raise soldiers for their armies and taxes to pay them. This made it harder to prop up dominoes along the edge of the steppes, and Roman and Han rulers watched in horror as their frontiers collapsed and great migrations spread diseases still faster. And as if all this were not enough, climate change also picked up its pace in just these years. From ice cores in Antarctica to peat bogs in Poland, climatologists see signs that the world was getting colder and drier. Global cooling shortened the farmers’ growing season, reduced yields, and set yet more climate migrants moving across Eurasia.

  Battered by migrations, disease, and declining yields, the complicated networks of tax and trade that had been built up by centuries of productive war began unraveling. In China, as tax revenues shrank and the costs of defending the frontiers grew, some second-century-A.D. civil servants started suggesting that the wisest path was simply to stop paying the troops. After all, they reasoned, the western border where Qiang rebels/invaders were doing so much damage was a long way from the capital at Luoyang; how bad could things get if the government simply left the army to fend for itself?

  The answer: very bad indeed. Soldiers turned into bandits, plundering the peasants they were supposedly defending, and generals turned into warlords, obeying only those orders that suited them. “These strongest and bravest of the empire,” the official Gong Ye noted, “are dreaded by the common people.” In A.D. 168, with the plague raging everywhere and the army disintegrating, palace eunuchs launched a coup against the twelve-year-old emperor and the circle of friends and in-laws who controlled his policy. It was a disaster. Government broke down altogether as civil servants murdered each other by the thousands in purge and counter-purge. Law and order began collapsing too, and rebellions claimed uncounted lives through the 170s and 180s. In 189, the most terrifying of the warlords on the western frontier marched on Luoyang, torched the city, and kidnapped the latest boy-emperor (this one just eight years old).

  For the next thirty years one strongman after another plundered his way across the realm, claiming to be restoring it, until in 220 the Han Empire finally split into three warring kingdoms. The frontiers dissolved, hundreds of thousands of Qiang and central Asian nomads migrated into northern China, and millions of ethnic Chinese fled from northern into southern China. Officials stopped even trying to count the dead.

  Rome fared just as badly. With population, agriculture, and trade in free fall, cash-strapped emperors stinted on soldiers’ pay or debased the coinage to make their limited stock of silver go further. The result, predictably, was that worthless coinage set off vicious inflation, depressing the economy even more.

  Angry soldiers took matters into their own hands. In A.D. 193 and again in 218 the imperial guard sold the throne to the highest bidder, and between 218 and 222 the empire was ruled—if that is the right word—by the crazed teenager Elagabalus, who stood out even among Roman emperors for his corruption, cruelty, and incompe
tence. Between 235 and 284, Rome had, depending on how you count, as many as forty-three emperors. Most were military men, and all died violently except one, who was carried off by the plague. Of the other forty-two emperors, Gothic invaders killed one in battle, and the Sasanid Persians captured another, whom they threw in a cage, mocked, and tortured until they got bored and murdered him. The remaining forty were all killed by fellow Romans.

  Forced to face multiple military threats, emperors had no choice but to entrust large armies to subordinate generals, even though these subordinates repeatedly repaid their rulers’ confidence by launching coups (this even though hardly anyone survived promotion to the purple by more than a few months). Once a general rebelled, his army would normally abandon its post on the frontier so that it could wage civil war, leaving the empire open to anyone who wanted to enter.

  The Goths built ships, sailed over the Black Sea, and looted Greece. The Franks (then based in what we now call Germany) rampaged across Gaul and into Spain. Other Germans raided Italy, while Moors overran North Africa and Sasanid Persians burned Syria’s prosperous cities. Realizing that the central government could not or would not protect them, the eastern and western provinces formed their own governments, and in A.D. 260 the Roman Empire—like the Han—split into three smaller states.

  The bloody breakdown of great empires was becoming the norm. India’s Kushan Empire, defeated by Sasanid Persian armies and Scythian raiders, split in two in the 230s. The western kingdom was absorbed by Persia after a final defeat in 248, and in the 270s the eastern kingdom shrank to a rump after losing control of the Ganges cities. Farther south, the great second-century trading kingdom of Satavahana also struggled to handle the Scythians, and in 236 it too collapsed.

  Mancur Olson, the economist from whom I borrowed the term “stationary bandit” in Chapter 1, liked to draw a contrast between these relatively benign thieves and completely malign “roving bandits.” Whereas stationary bandits came, saw, conquered, and administered, roving bandits came, saw, stole, and rode off again. The empires of the first millennium B.C. flourished largely because their stationary bandits were usually strong enough to keep roving bandits out, but by the third century A.D. this was no longer the case. Almost everywhere in Eurasia, war turned counterproductive, tearing the huge, peaceful, and prosperous ancient empires apart.