Terrorism as but a small piece in the cycle of Violence?

Is terrorism caused only by the malice and hate of a few demented people? or are there more factors in their existence than just their bad ideals and actions?
Terrorism exists as a reaction, not as a first hand action. Yes, it is wrong that civillians die, that innocents are killed, that there is reckless hate for an ideal. But I do not think terrorism would exist if it werent for the bad actions to cause reactions. For example the situation of Al Qaeda. They have terrible effect on society all around the world from blowing up buildings all around the world, to oppressing whole cultures into living in fear. I am not justifying their terrible actions, but I am stating that they are not the only ones doing wrong. I think that they are only motivated into existence by US invasion of what hey consider their land. There are many documentaries which show US's disregard for innocent people in the wars in the middle east, for example the real footage documentary Restrepo. Al Qaeda are pushed into existence by previous injustices, not entirely up to them, which they choose to respond to violently.

Al Qaeda would probably not exist if they had nothing to respond to, no previous deaths and violence inflicted upon their own people to avenge. They are terrible, violent, and cause huge amounts of harm and terror, no matter how much they may argue that they are freedom fighters. However, they are not the start of violence, they are just part of a continuing cycle of violence. That is why the situation in the middle east is very ironic: the USA is fighting a war in Afghanistan to "end terrorism", when probably the best thing to end terrorism is to not face and escalate the conflict, but pull the troops OUT. Peace would partially solve the problem the US is failing dramatically to solve with violence. By pulling the troops out, al Qaeda would have less to respond to, less to react to, and less of a base/founding ideology to push them in their terrible and violent resolve. Peace would destroy a large part of the base of this terrorist organization, leaving it weaker than even violence and war could.