Terrorism is not strictly a descriptive term. A terrorist is someone who wants to impose his or her political aims through fear rather than by persuasion and democratic choice. If he is operating in a non-democratic society where there is no opportunity for persuasion he might be considered a legitimate guerrilla or resistance fighter. The term may have been coined in the 19th century by Russian Anarchists fighting against the Tsarist dictatorship which allowed no political role for anyone other than the Tsar.

In democratic countries there are a number of terrorist groups which might in part be considered a mental health problem as they behave like certain types of religious cult and often do not respond to rational argument but pursue aims which are based on internal beliefs. For example, the Basque group ETA is fighting for an independent state although most Basques have voted to endorse the present devolved state and do not support the aims of ETA. The IRA is a similar group whose aims - a united Ireland - could only be achieved by persuasion. If they had succeeded by their recent methods it could only have been as a result of ethnic cleansing.

However, the main body of the IRA was persuaded to give up the fight by meeting real grievances: the low status of the Catholic citizens of Northern Ireland and the perceived dictatorship by the Protestants, addressed by laws and an elected assembly with a political system giving power to all citizens.

Other examples are in Corsica, Punjab, Kashmir, Sri Lanka, Aceh in Indonesia, Germany, Italy. Small groups have sometimes operated in the United States (consider the Oklahoma bombing of a Federal building - the act of anti-government fantasists). In Sri Lanka the terrorist group, the Tamil Tigers may have been defeated by the Sri Lankan army, but the underlying grievances they represented remain. The same is true of the Chechens whose longstanding opposition to rule by Russia has lasted for centuries.

The group or network inspired and perhaps financed by the late Osama bin Laden is the most prominent group at present (2009). One problem with these is that there are no obvious grievances that can be met to satisfy their wishes, which are largely fantasy: setting up a worldwide Khilafat - a global Islamic society of a medieval pattern. As the charter of one of these groups prescribes roles for slaves, it would seem rather repulsive to people in a modern western society. Does it reflect mainstream Muslim thought? That is a matter of dispute.

See also Terrorist wars