Terrorism has age-old origins. Mentioned by the ancient Greek historian Xenophon, terrorism may well have been practiced by the first humans to walk the Earth. As a means of frightening the opposition into surrendering, it has been a popular tactic in every era. As defined by the U.S. State Department Office on Counterterrorism, terrorism is premeditated, politically motivated violence that targets noncombatants in an effort to influence an audience. It is propaganda dependent upon violence to maintain fear.

Although terrorism is a worldwide phenomenon, it has roots in the Middle East. The first terrorist organization appeared in the first century when a Jewish sect known as the Zealots (Sicarii) promoted revolution against the Romans by killing Roman soldiers and Jewish collaborators. The Zealots committed mass suicide at Masada in A.D. 70. In 1090, a terrorist organization formed in the mountains of Persia. This group of Islamic extremists included Shiites who sought to keep Islam pure by killing prominent men from the Sunni branch of Islam. The Abbaside dynasty targeted by the Isamailis insisted that the terrorists were "Hashshishin" or under the influence of hashish. The term became the source of the word assassin.

By the middle ages, terrorist violence had spread to Europe. In 1605, the most famous act of terrorism in this era occurred when a Catholic attempted to assassinate Protestant James I of England. James had issued an edict banishing Catholic priests from England. Guy Fawkes, a Catholic, attempted to kill the king by placing thirty-six barrels of gunpowder under the houses of Parliament. He was caught while unloading the barrels, one day before the king planned to appear before the assembly. Under torture, Fawkes revealed the names of fellow Catholic conspirators, who were tried and executed. Guy Fawkes Day remains a popular British holiday.

In the New World, Europeans directed terrorism at Native Americans. Ethnic violence by the Dutch, Spanish, and British claimed many Native American lives with Native Americans retaliating by slaughtering some European colonists and kidnapping others. The Spanish conquistadors are known to have used rape as a weapon against Native American women. Rape as an instrument of terror had a long tradition in the Old World, with soldiers typically assaulting women in conquered areas. While there is no evidence that Native Americans sexually assaulted Europeans, colonists expected and feared such attacks. This fear of sexual assaults upon white women would continue to poison relations between Native Americans and the United States well into the nineteenth century.

With the end of the French and Indian War in 1763, the British needed to find a way to pay for the costs of the conflict. Unwilling to add to the burden of the British taxpayer, Parliament imposed the Stamp Act on the British colonies in America. The Americans did not want to be taxed without their consent. They tried peaceful protests and petitions before resorting to violence. Samuel Adams, a Bostonian opponent of the tax, decided to unite various city mobs as a weapon for demonstrating American opposition to the tax. He created the Sons of Liberty. Mobs that appeared in other cities were labeled Sons of Liberty, although they were not directly connected to the Boston group. These men roughed up tax collectors, invaded and wrecked the homes of British officials, and hanged tax collectors in effigy. The violence became so severe that few men could be found to serve as tax collectors. Conservatives who opposed the Sons of Liberty also resorted to violence. The White Oaks and Hearts of Oak clubs consisted of men loyal to England who posted themselves throughout Philadelphia to break up Sons of Liberty demonstrations. As the American Revolution progressed, both sides employed terror. The Americans who supported the British suffered vandalism and physical assault, while the revolutionaries were tortured and had their fields burned.

The French Revolution that began in 1789 involved several episodes of terrorism as France underwent a profound political and social upheaval. The revolution had began in a comparatively moderate fashion but became radical in 1791, when Paris militants forced members of the Legislative Assembly to schedule new elections. The Paris masses continued to remain anxious about the Revolution and, in September 1792, responded violently to rumors of counter-revolutionary plots. Crowds of workers, shopkeepers, and artisans stormed the prisons, from which they assumed thousands of royalists would escape in the event of a foreign invasion. Popular courts were improvised, which ordered the executions of more than 1,000 prisoners, many of whom were criminals and prostitutes.

These "September Massacres" were followed by the 1793–1794 "Reign of Terror." During the Terror, the Committee of Public Safety attempted to create a Republic of Virtue. All the people who did not measure up as sufficiently virtuous were to be executed. About 10,000 victims were arrested, interrogated, and guillotined. Most of the dead were politicians and aristocrats, including King Louis XVI and Queen Marie Antoinette of France, but the guillotined also included peasants who had refused to give food and farm animals to the revolutionary army. The execution of the king prompted the ruling monarchs throughout Europe to become much more autocratic in an attempt to prevent bloody revolutions in their own nations. When the Jacobins who conducted the Reign of Terror fell from power, they were attacked in the White Terror. This outburst of violence targeted the Jacobins and their supporters in the form of street fighting and massacres. More people died in the White Terror than in the Reign of Terror.

The United States, though horrified by the French violence, experienced its own terrors. While colonial America had been made up of diverse people, virtually all but the blacks and Native Americans possessed a northern European Protestant background. After the end of the Revolution, large numbers of Irish Catholics began to immigrate. These immigrants came under attack, both for religious reasons and for competing with native-born Americans for jobs. The Irish were quick to fight back. In New York in 1799, the Orangemen—Presbyterian Scots-Irish who had a long history of fighting with the Catholics in Ireland—mounted an anti-Catholic parade on St. Patrick's Day. In 1806, a New York Scots-Irish gang known as the Highbinders tried to storm a Catholic church. Both clashes resulted in deaths on both sides. In Boston in 1837, eight hundred state cavalry were needed to put down a street battle that began when a Protestant gang inadvertently bumped into an Irish funeral. And in Philadelphia in 1843, an anti-immigrant group formed to promote the idea of Protestant Bibles in the public schools. After much parading and counter-parading, a young Protestant was shot to death by Irish terrorists. A Protestant counterattack on a Sisters of Charity school the next day sparked a melee that killed two passersby and many combatants. In the next several days, the outnumbered Irish watched as two Catholic churches and a female seminary were burned to the ground, as rioters defied state troops. On July 7, 1843, a mob used battering rams to attack another Catholic church. Five thousand state troops were called in to halt the violence. The mob, unimpressed, fired a cannon at the soldiers with the soldiers firing volleys in return. The riot ended with two dead soldiers and thirteen dead civilians. Continuing violence between Protestant and Irish Catholics prompted many cities, including Philadelphia, to form police forces.

Meanwhile, Irish Americans combined with other whites to riot against the black presence in major Northern cities. African American communities in the North grew during the antebellum era as freed blacks and fugitive slaves fled from the South. This influx was resented by unskilled white workers and competition for jobs became more intense as the economy weakened in the 1830s. The growing abolition movement added to hostilities when black and white reformers, both male and female, gathered in public meetings. The mixing of the sexes and races in public raised sexual fears of miscegenation or race-mixing, and prompted mobs to burn down the halls in which the meetings were held. A July 1834 New York City riot set off by meetings to discuss the abolition of slavery turned into an orgy of violence that spread over several days and seemed designed to drive blacks out of New York City. The riot ended only when 1,000 militiamen answered an emergency call and were issued live ammunition with orders to shoot into the crowd. In Boston in 1835, Mayor Theodore Lyman was attacked and his office was stormed by a mob that also attempted to lynch abolitionist newspaper editor William Lloyd Garrison. This racial terrorism would ultimately culminate in the three-day-long New York City Draft Riots of 1863.

Terrorism is a popular political tactic because it often succeeds. Through the coming decades, terrorism would continue to be deployed around the world to influence politics, to end the perceived abuses of big business, and to remove the economic competition of minority groups.