We seek to find meaning in everything, and it is tempting as a policymaker or economist to attribute the terrorist attacks of September 11, 2001, to some particular motivation. An obvious candidate is the economic status and opportunity of groups that produce terrorists, but economists believe any connection between poverty and terrorism is probably weak at best.
As summarized here, researchers at the National Bureau of Economic Research have examined this question, whether development and terrorism are inversely related, and they have determined that the evidence of such a connection is weak. As Alberto Abadie remarks, political freedom is more closely related to terrorism.