Terrorism has been practiced throughout history and throughout the world.

The ancient Greek historian Xenophon (c. 431–c. 350 BC) wrote of the effectiveness of psychological warfare against enemy populations.

Roman emperors such as Tiberius (reigned AD 14–37) and Caligula (reigned AD 37–41) used banishment, expropriation of property, and execution as means to discourage opposition to their rule.

The Spanish Inquisition used arbitrary arrest, torture, and execution to punish what it viewed as religious heresy. The use of terror was openly advocated by Robespierre as a means of encouraging revolutionary virtue during the French Revolution, leading to the period of his political dominance called the Reign of Terror (1793–94).

After the American Civil War (1861–65) defiant Southerners formed a terrorist organization called the Ku Klux Klan to intimidate supporters of Reconstruction.

In the latter half of the 19th century, terrorism was adopted by adherents of anarchism in Western Europe, Russia, and the United States. They believed that the best way to effect revolutionary political and social change was to assassinate persons in positions of power.

From 1865 to 1905 a number of kings, presidents, prime ministers, and other government officials were killed by anarchists' guns or bombs.