As the second millennium closed, the talk in the capital city of the mightiest nation on Earth concerned the persistent problem of "hate crimes." American citizens in A.D. 1999 had been killing one another in horrific ways over trifling differences of creed and color, even methods of lovemaking. So one bright day in late October a group of the country's legal experts gathered to learn more about fighting hate.

Their leader, the highest law enforcement official in the land, declared her beliefs:

Hate is learned, she said.

Haters are cowards, she said.

And her most important point: If those who hate each other could only recognize their common human identity, to sit and talk and share their feelings, then they would begin to respect their differences. Hate would evaporate.

Her heart was in the right place and her message was inspiring. But from the perspective of 1,000 years of history, she was pretty much dead wrong.

Because of its persistent impact on world events, hate is among the best chronicled of human emotions. Certain conclusions are inescapable, supported by both the sweep of history and the observations of those who have made hate their scholarship:

Hate is innate. The capacity to hate is central to our being; aggression is necessary for our survival. Yes, one can learn to hate, but it is the wiring in our brains that makes this almost a default process, permitting ordinary people to easily adapt to mass-killing projects. It has happened in societies spanning the globe, and the millennium.

Haters are not cowards. They are bold. They make good leaders. They build empires; they are celebrated for their zeal. As the writer Henry Miller observed: "The men who are most honored are the greatest killers. They believe that they are serving their fellow men."

Familiarity tends to breed hate, not eradicate it. Interaction among cultures has often proved disastrous. Mankind's aggressive expansion has been the major story of the past 1,000 years; the results are brutally obvious. The more we get to know the Other, the more we are inclined to fear, attack, despise and destroy him.

Timur the Terrible

He liked to build grand towers of human heads -- he mounded them carefully to resemble minarets, the better to glorify Islam and the Prophet Muhammad. In 1387 he exterminated 70,000 residents of one Persian city and piled high their freshly severed heads. It was probably his most flamboyant show of cruelty since the time he bricked 2,000 prisoners into a tower and left them to die.

He was a Turkic-Mongol warrior who walked with a limp -- known as Timur the Lame, or Tamerlane. In 1590 Christopher Marlowe published a play about him, called "Tamburlaine the Great," and quotes him thus:

"Our conquering swords shall marshal us the way

We use to march upon the slaughter'd foe

Trampling their bowels with our horses' hoofs . . ."

Timur is ranked by some historians as the most hateful militarist in history prior to the arrival of Adolf Hitler. It is said that he once had a suspected traitor boiled alive before him in a copper kettle. When faced with the problem of transporting 100,000 Hindu prisoners of war, he decided all should be "food for the sword."

As he once decreed: "Infidels should all be dispatched to hell with the proselytizing sword."

Several other quotes survive from Timur (1336-1405), but perhaps the most telling is this one:

"I am not a man of blood; and God is my witness, in all my wars I have never been the aggressor. My enemies have always been the authors of their own calamity."

The Bloodiest Century

Haters love to hate. Most just don't like to admit it. Few political leaders would espouse a direct platform of hatred toward others. It's an unseemly emotion. Those who froth in rage are considered unstable.

Instead, leaders have cloaked their contempt in higher motives; they perfume their vitriol with virtue: The enemy must be defeated for the greater good. ("We should bury bronze tablets saying it was we, we who had the courage to carry out this gigantic task!" exulted one German officer. It was 1942. He was talking about the Polish death camps.)

John Adams once observed: "Politics, as a practice, whatever its professions, has always been the systematic organization of hatreds."

Nowhere is the evidence more persuasive than in the past century, which ranks as the bloodiest in terms of lives lost to genocides and various ideological campaigns. Tally the tens of millions of victims of Mao, Stalin and Hitler -- ranked by some historians in that descending order on the scale of all-time evil -- and you are left to wonder whether civilization has progressed at all since A.D. 1000, except in terms of its technologically advanced killing capacity.

The cliche about "ancient hatreds" arises in news coverage of most modern conflicts for a reason: Rarely do long-term antagonists learn to love and forgive. But hate's dark role in history often is offset by its modernizing, even civilizing influence. Yes, hate has conquered peoples, and enslaved them. But in so doing it has spread culture, pushing societies across borders and oceans, pollinating ideas, opening new routes for trade. It has propelled commerce, industry and communication.

In the past 10 centuries, hate has helped to propagate major religions (Christianity, Islam) and moral codes. It has brought forth enduring artistry. Hate attended the birth of the world's greatest democracy. (The American colonists vilified George III, the king of England in 1776, and called his ministers "monsters in the shape of men" -- they embodied the beasts of the Apocalypse described in the Book of Revelation.) But for the many episodes of hate in this century, we might not have the concept of "human rights" nor punishment for "war crimes."

Not all killing is hate-driven, of course. Neither is all war. Decent people need to defend themselves against aggression. Many soldiers do not hate their enemies, per se. It is their duty to kill.

Scholars who have studied warfare agree that when human beings engage in systematic campaigns in which they must kill, something significant happens: a detachment, a numbness to emotion. The enemy becomes less than human. In cases of genocide, the distinction is exaggerated. Enemies are viewed as animals, insects, vermin to be eradicated. This permits ordinary people to embrace a degree of savagery that would otherwise seem unthinkable.

The second millennium's many spasms of violence are distinctive for their unspeakable brutality against civilians. The Crusaders in the 1100s roasted the babies of heretics on spits. In 1999, the rebels in Sierra Leone sought out young children, chopping off their arms and hands.

Born to Kill

Why do we hate? We hate for the same reason that we love. Because we are human.

Let's begin with an image as old as time: a baby nestled in his mother's arms. Let's say this child was born on the steppes of Central Asia in the year 1190.

The human infant can instinctively distinguish between caregivers and strangers very early. Babies will cry at an unfamiliar face. This is a gift of our nature. By 6 months, a baby knows the difference between friend and foe. Our minds also tend to categorize: Red/blue. Short/tall. Us/Them.

This mechanism also is what allows us to hate. We have the ability to identify the Other.

Our child of the steppes -- a Mongolian -- doesn't hate anybody. Yet. Like everyone, though, he is born with a brain that harbors aggressive impulses. In threatening situations, humans, like animals, calculate the options of flight and fight. A constant inclination toward flight -- or fear -- is counter-evolutionary. Those who slither away or allow themselves to be vanquished will not thrive.

Higher animals are a xenophobic and truculent sort. Sociobiologists tell you that man has evolved -- survived -- because he's always been a fighter.

Our Mongolian child is born of nomads. They are tough stock. They drink the blood of horses. They are excellent archers. They scorn the peasants who are bound by the land. They are despised in return.

For Mongol youth, it is a time of great opportunity. Nearly everyone is joining the army of the great tribal leader Genghis Khan. Our Mongol child does, too, when large enough to hold a sword and ride at a gallop. Khan has enlisted nearly the entire population of 1 million.

It takes a strong leader to unite his people. Someone who isn't afraid to identify enemies and make them scapegoats. Someone who has a vision of national glory, an appetite for power and a taste for blood. Someone like Khan, who said he was happiest when killing.

"Man's greatest good fortune is to chase and defeat his enemy, seize his total possessions, leave his married women weeping and wailing, ride his gelding [and] use the bodies of his women as a nightshirt," said Khan.

He nearly exterminated the Tatars, a rival tribe that had killed his father. Khan claimed to have a heavenly mandate. He believed the Mongol people alone were fit to rule the Earth. He built their tribes into a military force that established the largest land empire of all time.

It made sense to get with the program. People in every age support causes out of self-interest; Khan revolutionized trade and communication, creating marvelous ground-floor opportunities for lucky members of the Mongol horde.

By some estimates, Khan and his Mongol successors (Timur claimed to be one) killed 30 million Persians, Arabs, Hindus, Russians, Chinese and Europeans.

As in Khan's era, people everywhere tend to defer to authority figures. They like to please the boss. Add in a few other factors -- an economic crisis, or a famine, a persistent strain of prejudice, a steady drumbeat of propaganda, the will of God -- and you can easily see why the march of history is accompanied by a steady flow of bodies into the abattoir of hate.

Throughout history, most killing has been done by regular people, just going with the program.

By 1215 our little Mongol baby is a soldier for Khan. He will help make the streets of Beijing slick with Chinese entrails.

The Rabid Reformer

He had a strong, Teutonic face -- wide forehead, large nose -- and favored monkish garb, perhaps a carry-over from his days as a priest. He had a fiery, revolutionary mind: His study of Scripture sparked the most significant religious upheaval of the millennium.

Martin Luther, the great reformer, brought millions closer to God by knocking down barriers to salvation. In the early 1500s, he preached that faith alone -- not the dispensations of a priest or donations to the church -- could save a sinner's soul. God loved all men freely and unconditionally, said the father of Protestantism.

There were a few important exceptions. The pope, of course, was the Antichrist. And the Jews, said Luther, were "devils" -- utterly detestable.

"Did I not tell you earlier that a Jew is such a noble, precious jewel that God and all the angels dance when he farts?" Luther scoffed in his 1543 tract, "The Jews and Their Lies."

"What shall we Christians do with this rejected and condemned people, the Jews? Since they live among us, we dare not tolerate their conduct, now that we are aware of their lying and reviling and blaspheming."

Burn their homes and synagogues, Luther urged followers. "I advise that their rabbis be forbidden to teach henceforth on pain of loss of life and limb." His final solution: "Eject them forever from this country."

God Wills It?

For much of the millennium there has been a disturbing but undeniable nexus between religion and hate.

Dieu li volt -- "God wills it!" -- was the battle cry of the First Crusade, launched from Germany in 1095. The Christian warriors hacked apart Arabs and Turks -- "that vile race," in the words of Pope Urban II -- on their way to sack Jerusalem, where Jews also were slaughtered. "Piles of heads, hands and feet were to be seen in the streets," reported the cleric Raymond d'Aguilers. "Men rode in blood up to their knees and bridle reins. Indeed, it was a just and splendid judgment of God."

The Crusades provide a model for many modern hate movements. The enemy was not just a sullied and worthless creature, but an agent of sin and evil.

In 1209, the town of Beziers, France, was known to harbor a group of religious freethinkers called the Cathars. They liked sex but didn't like marriage. They gave women roles in the ministry. They believed in reincarnation. They practiced vegetarianism.

They were, according to the Catholic Church, "vile animals" and "pests." The pope launched a Crusade against them, offering indulgences to anyone who killed a Cathar.

At least 15,000 men, women and children holed up in Beziers, many seeking refuge in the churches. The military commander of the siege wondered how to tell the heretics from the true Christians. He consulted the pope's local representative for advice.

"Kill them all," ordered the papal legate. "God will recognize His own."

`Why I Shot an Abortionist'

Nine hundred years after the First Crusade, a man named Paul Hill takes his wife and three young children to the beach in Pensacola, Fla. He is thin, sandy-haired, meek-looking; he wears big eyeglasses. The Hills and their young daughters and son splash about in the clear, warm water and frolic on the sugar-like sand. The perfect end to a busy week, he thinks.

Paul Hill knows this might well be the last time he will enjoy such simple pleasures with his family. But he has an important task ahead of him, a glorious task commissioned by God Himself.

"Who was I to stand in God's way?" he would later write. "He now held the door open and promised great blessing for obedience. Was I not to step through it?"

On July 29, 1994, Hill -- a former Presbyterian minister -- drove to an abortion clinic and shotgunned to death an arriving doctor and his escort. He was condemned to death row. He later wrote a letter to his supporters, titled "Why I Shot an Abortionist." It was, naturally, distributed on the Internet, and was cited in a booklet distributed at the federal hate crimes conference in Washington.

"Inner joy and peace . . . have flooded my soul," Hill declares in his letter. "The Lord had done great things through me."

Here we find two unmistakable messages. In various forms, they have spanned the millennium:

I was only following orders. And:

We do not hate. God hates for us.

The Risk of Faith

In 1597, Jesuit missionaries went to Japan to save souls. The Japanese cut their ears off. Then 26 clerics were strapped to crosses and lanced to death.

The Puritans sailed to Massachusetts to escape persecution, then set about persecuting those who didn't share their beliefs. They whipped Quakers and cut off their ears. Some were hanged.

In Europe and the New World, tens of thousands of women were burned alive based on accusations that they were witches who copulated with Satan. And also rode in the sky on brooms.

Native people in the New World had their own religious traditions but were deemed disposable heathens when they refused to be Christianized. "Merciless Indian savages," the Declaration of Independence called them. They were killed, enslaved and forcibly relocated.

Followers of an American preacher named Joseph Smith called themselves "saints" and believed in the newly discovered Book of Mormon. In 1837, the governor of Missouri ordered them expelled or exterminated "for the public good," stating, "Their outrages are beyond all description." At least 17 Mormons were massacred by the local militia.

In China, the Society of Harmonious Fists blamed Christian missionaries for drought in the late 1890s, declaring: "The Catholic and Protestant religions are insolent to the gods, extinguishing sanctity, rendering no obedience to Buddha, and enraging Heaven and Earth . . . But 8 million Spirit Soldiers will descend from Heaven and sweep the Empire clean of all foreigners!"

During the so-called Boxer Rebellion at the turn of the last century, scores of Christians ("first-class devils") and their converts ("second-class devils") were summarily executed. Their heads were displayed in cages.

Of course, religion does not always stand for hatred; most religions preach love and tolerance and within them are many who seek social justice, alleviate suffering and spread joy.

In July 1900, in the province of Shansi, a missionary named Mrs. Lovitt, in handcuffs, addressed her persecutors. "We all came to China to bring you the good news of the salvation of Jesus Christ," she said. "We have done you no harm, only good. Why do you treat us so?"

Whereupon a soldier solicitously removed her spectacles, and then, with two quick strokes, sliced off her head.

The Forgotten Slaughter

The women gathered by the roadside -- cursing, screeching, mocking -- as the prisoners filed past: Behold the scum who stand in the way of progress and civilization. They are parasites, the enemies of the people.

The women were Turkish; the objects of their scorn were Armenian. A pastor taken captive later wrote of hearing "the ancient battle cry of the women of Islam -- the exultant lu-lu-lulu filled with the concentrated hate of the centuries." A few days earlier, Armenian churches, homes and schools had been plundered; 1,500 Armenians were killed. It was November 1895, the era of the Young Turks -- who marshaled nationalist fervor and religious zeal toward a typical end. "We are all equal, we glory in being Ottomans," declared one Young Turk leader.

Armenians didn't belong in the empire. So, by 1915, genocide happened:

"Officials -- military officers, soldiers, shepherds -- vied with one another in their wild orgy of blood, dragging out of the schools delicate orphan girls to serve their bestial lusts, beat with cudgels dying women or women close on childbirth who could scarely drag themselves along," wrote a German eyewitness to President Wilson.

"And so they drove the whole people -- men, women, hoary elders, children, expectant mothers and dumb sucklings -- into the Arabic desert, with no other object than to let them starve to death."

Between 800,000 and 1.5 million Armenians were wiped out. The world hardly cared or noticed. The Turks steadfastly denied it. In 1939, instructing his officers to kill Polish women and children "relentlessly and without compassion," Adolf Hitler assured them that history would not judge them harshly. After all, he said, "who remembers now the massacres of the Armenians?"

When we in modern culture conjure an image of a "primitive" people, one standard scene arises: the savage in the jungle, holding a string of shrunken heads. Anthopologists and other academics seem to delight in studying the head-hunters' warrior customs.

One much-studied tribe is the Mundurucu of Brazil, who, before the arrival of Europeans, focused their social lives and culture entirely on aggression. In a typical raiding party, the Mundurucu men would gather at dawn, shoot flaming arrows into the thatched huts of a sleeping, rival tribe, rush in screaming, and behead as many men and women as possible.

Some experts speculate that the tribe killed to increase its own chance of survival, but others say head-hunter behavior is simply emblematic of human nature. The Mundurucu language gives a clue: They described their victims in terms normally used for animals, such as tapir and peccary.

They also had a word for those who were not members of their tribe. It meant, simply, "the enemy."

`Bad Elements'

Just as people of faith embrace visions of paradise, the leaders of secular movements frequently advocate the same goal. They, too, harness hate to achieve their aim of a utopian world.

Some anoint Karl Marx, an atheist, as the man whose ideology inspired the greatest number of "unnatural deaths" in modern history: well over 100 million. His theories were just that; they failed miserably in practice. Communism was supposed to result in a harmonious society where all would share, none would go hungry or otherwise suffer. It led to hate-fueled revolutions, purges, forced famines, genocide, torture.

"We stand for organized terror . . . terror being absolutely indispensable in current revolutionary conditions," proclaimed the first head of the Cheka, the Bolsheviks' secret police. Lenin's revolution set an amoral tone that allowed communist movements throughout the 20th century to scapegoat and kill with abandon.

China's Chairman Mao hated "bad elements." He kept a shifting list of "class enemies," including imperialists, intellectuals and landlords; in Cambodia in the early 1970s, Pol Pot executed anyone who didn't embrace his new society, including those who lived in cities or wore eyeglasses. Stalin starved millions of peasants to death. All three leaders claimed to be laboring in service of the masses: terror for the benefit of all.

We Are the Enemy

Is there no hope?

Historians who survey the evidence of the last millennium don't see much. For scholars, man's capacity to hate, and act on his hate with extraordinary brutality, seems undiminished by time, or technology, or advances in moral thought. Perhaps the best that can be said is that societies seem, at long last, to have at least defined the enemy as ourselves, and some target hatred as a blight to be exterminated, if only we could.

Hatred among humans is like a strange disease. It is both congenital and infectious. The infectious part is, in some ways, worse.

In 1911, a German scientist journeyed to the coastal colony of South-West Africa (now called Namibia) to study the offspring of the sexual unions of white German settlers and native African women. Eugen Fischer, a geneticist at the University of Freiburg, was, like the colonists -- and like many Europeans and Americans at the time -- an unabashed racist.

He concluded that the ethnically mixed children -- "Hottentot bastards," as he called them -- were inferior in every way to their German parents. This was hardly surprising. The Germans considered blacks to be subhuman. They were notorious for abusing a particular tribe of cattle farmers, the Herero, plundering their lands, calling them baboons, lynching them, raping them.

In 1904 the tribe struck back, killing German farmers. In reprisal, the Kaiser's army set out to exterminate the entire tribe. "Every Herero found within German borders, with or without guns . . . will be shot," Lt. Gen. Lothar van Trotha ordered. When they fled into the desert, he poisoned the water sources and left them to die by the thousands.

Many Africans who surrendered were worked to death or put in concentration camps, where they perished of tuberculosis and typhus. By 1907, only about 15,000 Herero -- out of an estimated 80,000 -- remained.

This episode, mostly forgotten, is regarded by some historians as the first true genocide of a century of genocides.

Professor Fischer's book, "The Principles of Human Heredity and Race Hygiene," caught on in Germany. In 1923, a copy reached an inmate who was serving a sentence for treason at Landesberg Prison in Bavaria. A failed artist and former corporal in the German army, the prisoner read hungrily about the theories of racial pollution and subhuman peoples. It validated his own thinking, and gave him some new ideas.

He decided to include these ideas in his own book, the one he was busy writing, called "My Struggle," or, in German, "Mein Kampf."