Terrorism

What is the cause of terrorism/resistance? I think it may be a bit more complex than it sounds

Because I suggest few of the areas with terrorism are recently invaded and numerous areas of recent invasion are not sites of terrorism. The countries involved don’t seem to be particularly repressive and the most repressive countries don’t seem to have much terrorism. This leaves me very reluctant to see terrorism as some sort of natural righting mechanism.

Trying to see what is the cause of resistance/terrorism itself. It seems to me like something that can be whipped up in any society regardless of the circumstances.
However in general the below seem to be indicators

1) It is often related to where there is a large group they identify with outside the country and where that group promotes the image that they are being wronged. (Communist groups, Palestine, srilanka, nth Ireland Thailand Chechnya bail etc) very few don’t seem to fit that prototype.
2) Quite often there is a fairly rapid rise in the population of the group from which the protagonist’s spring.
3) The country is often on the boarder of the Islamic world (there are few reasons behind this rather than it being intrinsically Islamic)
4) Communists are sometimes involved (I think the Soviet Union started this ball rolling)
5) The government is generally reasonably democratic

people who are engaging in terrorism tend to feel they are being "occupied" but that term means very little more than "I hate the government and will resist them" and possibly "I hate the foreigners more than I hate my neighbors" rather similar to tax is theft or property is theft.

Anyway what do you think is a root cause of terrorism?
Preferably with some consideration of when that rule created terrorism and where the absence of it didn't create terrorism