There is no agreed-upon definition of terrorism, but most agree that it is collective, not individual; it is political, not criminal (although some terrorists morph into criminal); it is covert; and it is violent, the violence striking without warning and often victimizing indiscriminately officials, combatants and non-combatant civilians alike, including those belonging to groups the terrorists stand for. In the confrontation between insurgents and states, between challengers and regimes, terrorism is one of several modes of confrontation ranging from peaceful and conventional political action to extremes of collective violence.
State terrorism occurs when a regime resorts to mass violence and extra judicial killings (as with assassination squads) against its own citizens, non-combatants and insurgents alike, as happens in violent conflicts between a regime and an ethnic, religious or national minority. There is a huge literature on ethnic cleansing, mass violence and genocide (cf. Benjamin Valentino, Final Solutions. Mass Killings and Genocide in the 20th century, 2004) and on mass killings, crimes against humanity and war crimes in political science, international relations and law (I review this literature in Conflict Theory, in Leicht and Jenkins, eds. Handbook of Politics, 2010 )
The theory of collective action is an appropriate tool for explaining the entire spectrum of challengers and unconventional confrontations: dissidents, mass protests, social movements, guerrillas and insurgents, including terrorists and state terrorism. The four dimensions of collective action are 1. discontent 2. ideology feeding grievances 3. capacity to organize 4. political opportunity. Each dimension can be unpacked with a number of cause-effect mechanisms and sub-theories. The blocking variables are the dimensions of social control, which also can be further specified. What the theory seeks to explain is under what circumstances some challengers become terrorists, who they are, their motivations, their belief system, how they recruit and organize, their leadership, support groups both internal and external, bystander publics, and what the response of the social control agencies and regime will be. Social control focuses on regime capacities, legitimacy, the security forces, support groups and publics, and the like. The dynamics of the contention (conflict and conciliation dynamics, strategies of confrontation the adversaries use; what actually happens by way of violence, conflict management, external support and intervention, outcomes) draws on both conflict theories and collective action theory.
I have described how the theory of collective action can be used to explain terrorism in general and for specific instances, the IRA, Palestinian insurgents and terrorists, Islamic jihad and al Qaeda [Anthony Oberschall, “Explaining Terrorism: the Contribution of Collective Action Theory” Sociological Theory 22:1, March 2004]. Since my article, there has been a huge increase of empirical research on terrorism and there exists a sophisticated literature in the social sciences which applies the theory of collective action and conflict dynamics to insurgency, terrorism and counter-terrorism [cf. M. Sageman, Understanding Suicide Networks; S. Kalivas, The Logic of Violence in Civil War; R. Alt and L. Richardson, eds., Democracy and Counterterrorism; C. Ankersen, ed. Understanding Global Terror]. To discuss and debate the topic of terrorism concretely and usefully, knowledge of at least some of these and similar sources is advised.
On social change and consequences, it is difficult to find a positive outcome, either for the terrorists achieving their primary objectives, or for the regime, state or target groups. Al Qaeda did not drive the U.S out of the Middle East, and the politics of fear in the U.S. have led to security institutions that have diminished democracy, civil liberties, and the rule of law. In Western Europe, Islamic jihadists have been contained; there has also been an increase in security institutions, but civil liberties and the rule of law have diminished less than in the U.S. In Northern Ireland, the provisional IRA gave up on terrorism prior to the start and successful conclusion of the peace process. Chechnya is ruled repressively, and Russia remains autocratic. The Tamils in Sri Lanka remain an underprivileged minority. The military in Algeria has repressed the Islamic jihadists and is the only North African state without an Arab Spring. The Palestinian fighters including Hamas are worse off than in 2000, the Israeli settlements have grown in the West Bank, the peace process is in shambles and the Israeli government is less ready to negotiate a two state outcome. Islamic jihad has been defeated in Indonesia and the Philippines. In Iraq, U.S. overthrow of Saddam Hussein’s regime and military occupation unleashed terrorism by many groups, including the state, with no end in sight, and there is high risk of civil war. State terror succeeded in Darfur, Syria is uncertain, other instances might be mentioned, and analyzed in depth. Superficially it looks like terrorism is a loss/loss outcome (with huge costs) in challenger-regime confrontations. Compared to other modes of challenge, it does not stand up.