Coercion hypothesis
Pain, casualties are caused to frighten governments into bending to the terrorist's will. eg US withdrawing from Middle East
Damaging an economy to weaken its country's ability to intervene in international affairs.
To recruit potential members into joining their movement through the attention violent attacks generate.
Violent acts pursue their own, often local, goals. In turn receiving support from other terrorist organisations.
Damage Hypothesis
Rally hypothesis
Franchise hypothesis