Well, I can't explain it all, it's a variety of factors that plays around everything. But there's a strong point that indicates the stronger violence from extremist groups after Gulf War I. This has also been ignited cause of the many US-Troops being present in the middle east
(their holy land) and American top officials mixing in with Saudi top officials ......which indeed gives an impression as of a hostile take over from foreign countries.
AQ + Taliban / I'm not sure to what extend these organisations still exists or whether it are splinter groups with same ideals working right now. In my opinion, people scream out AQ or Taliban, but personally I think it are splinter groups.
As with all fundementalists (and also the American fundementalist Christians) they have their 'own' ideas about the world. Leaving them in their own world, they will not do alot of harm / but when threatened for having to give up their ideals etc. etc. they sure will strike hard. Invading their 'holy land' really set it off.
Personally I see any fundamentalists groups right now as the Catholic church was WAY WAY back in the middle ages. They need time to grow, and develop.
The following link I found interesting in regard to your question about ideology
http://www.danielpipes.org/article/1056Combating the Ideology of Radical IslamAlso I urge you to find some time to watch the following documentary in regard to the appearance of the Carlyle group right after Gulf War I. First coupla minutes in Dutch, the rest is in English. It's about the Carlyle group but matches up nicely with your question.
http://cgi.omroep.nl/cgi-bin/streams?/tv/vpro/tegenlicht/bb.20030516.rm