Take a closer look at the groups that use terrorism as a method of fighting against empires of government. When you think of al-Qaeda, Hezbollah, Hamas or the Sunni insurgency, we think of car bombings, roadside bombs, and suicide bombers. Those who are willing to fight in that manner, to target women and children, to target those who believe the same religion as they do - these are the characteristics of a fanatic. They believe strongly enough in their cause that they are willing to do anything to fight for it. Terrorism to them is just a method of carrying out that fight.
They do not need advanced weapons or expensive ones, or even that many of them in order to commit these acts. They are hard to catch as they do not fight in the open, army to army. And they receive both attention and response so disproportional to their military strength and skill because of the horror of their attacks that they feel they are being effective.
There is no one correct answer to this question, but here are some suggestions. First, some people use terrorism to create fear in an effective way. I say that terrorism is effective, because you are largely fighting an invisible enemy. This fact is very scary. Second, some people use terrorism to carry out strategic attacks on places that are symbolic. For instance, it is not chance that the NY and DC were targets on 9/11. Finally, I think that people use terrorism, because there is little else that they can do in terms of power. Without a standing army, you really cannot wage a traditional war.
We, the target victims, are the ones who call them "terrorists." They do not see themselves as such. They are a completely unique subculture of fanatics who believe that what they are doing is correct, that their targets are the enemy, and that attacking them will bring them some form of benefit.
That sort of negative motivation comes from the training these subgroups receive. It is a type of brainwashing no different than a hardcore sect. They are physically and mentally conditioned to stick to their system of belief, and that is why they start many of their representatives at a very young age.
What can u do with an 8 year old who has been told that America is evil, and that our way of life should be terminated? Add to that the amount of consistent persuasion, the promise of a glorious ending, and monetary funding to your family should you become a suicidal bomber?
It is the reality that we must face: They are bound to their belief systems and they are not willing to change that. Therefore, they are willing to fulfill every expectation placed upon them and, on top of that, they are told that what they are doing is honorary.
Post Note: I was due in Afghanistan at the first of the month, when all sort of killings broke lose. I received the same amount of information about the Taliban as maybe they got about us. However, isn't that interesting that (in our mentalities,) we STILL could not fathom even facing or confronting them the same way they do US? It was out of the question! In fact, we became more educated on THEIR way of life than they were on OURS. This may be a sort of example to differentiate between a culture and a subculture.
You do not tell us which groups, but in my opinion, the main reason groups come to use terrorism is that they are too weak to do anything else. Terrorism is a last resort type of tactic. Groups that have better ways of achieving their goals do not use it.
You can see that none of the terrorist groups are strong in comparison to countries. Al Qaeda cannot hope to attack America militarily, so what is it supposed to do if it wants to hurt us? It can't launch missiles so it has to do terrorism.