"People join extremists organisations for quite a number of reasons. Some - especially those locally recruited - mostly join for economic benefits." Mahdi Abdile is Finn Church Aid’s Regional Representative for East and Southern Africa. European Institute of Peace.
In countries where opportunities are scarce, weak governments and unprotected human rights, terrorism is an opportunity for destabilizing the status quo. Somalia, 27% joined al Shabab for economic reasons and 15% mentioned religious reasons. Once established 13% were forced to join.
Simon Cottee writes in The Atlantic "Since the 1980s, (the idea it is driven by individual pathology) has fallen into disrepute, and the scholarly consensus now holds that the roots of terrorism lie not in the individual, but in the wider circumstances in which terrorists live and act."
Noam Chomsky warns in an Alternet article, a false flag terror attack could be staged as Donald Trump supporters realize he can't fulfill his promises.
Between, inequality, despair and corruption, terrorism is a strategy for those who have power over the masses to further alienate people from peaceful civil structures to centralize power, further the feelings of powerlessness and create new (or old) scapegoats.