Terrorism, in various forms, has been practiced throughout history and across a wide variety of political ideologies. There are as many definitions for the word terrorism as there are methods of executing it; the term means different things to different people, and trying to define or classify terrorism to everyone's satisfaction proves impossible. However, most definitions of terrorism hinge on three factors: the method (violence), the target (civilian or government), and the purpose (to instill fear and force political or social change).

The adoption of terrorist techniques by insurgent groups, especially in the developing world, has led to a perception of terrorism as a natural outgrowth of the anticolonial struggle, merely another weapon of revolutionary guerrillas in their campaigns for independence. This understanding—or, in the eyes of many terrorism experts, misunderstanding—of the term terrorism is also expressed in the old cliché, “One man's terrorist is another ...