Terrorism is a deliberate form of political or ideological warfare waged by fanatics with a disposition for unlimited violence. In the case of extreme religious terrorists, whether Islamic or Christian or Sikh, they are engaged in a holy war, a struggle for the fate of the world that justifies any amount of bloodshed. Good point. I would add that many of those with "a disposition for unlimited violence" simply love violence. Any grievance will serve to justify blooshed. They don't really need a reason, just the means and the opportunity.