MrsTerryPratchett I DON'T agree with these maniacs but can people understand why there is so much anger? Rendition, drones, the Gulf Wars (note the plural), racism, Islamophobia, violence against Muslims, Guantanamo
The above are all recent things that have been used to whip up increased fervour and justification. The roots of Islamic Jihad started much much earlier (one could in fact say in the 7th Century) but the modern revival was in the 50's by Qutb, who later joined the Muslim Brotherhood.
It is worth reading his exegis of the Quran "In the shade of the Quran' where he concludes that violent offensive jihad against unbelievers and Muslim governments that haven't implemented true Sharia is a mandatory religious requirement, as only this will return muslims from their present day state of Jahilya (ignorance) where they trail behind the West, and restore the Islamic world to the pre-eminence and glory it enjoyed immediately after Islam's initial spread.
Here is an English translation for those who are interested:
tafsirzilal.files.wordpress.com/2012/06/at-taubah-eng.pdf
Westerners are making a serious error by only selectively listening to what the Jihadi's themselves are saying. Their motivations are not just in response to western foreign policy. If they were, there would not be the forced conversions, persecution and barbarity towards the minorities, who have of course not done anything to them.
They are doing this to fulfil their duties as 'true muslims' as instructed for them to do so by the Quran and by the prophet Muhamed's example, who used extremely similar methods. They are driven to implement Allah's Laws, initially in existing muslim lands, and later in non-muslim ones.