Theological hatred right out of the Dark Ages, and following the ancient model, willing to kill anything in sight.

I personally think that the causes of this perceived 'war' are purely political. Religion is simply a recruitment tool. Islam is one of the most tolerant religions around, based upon their scriptures, but like Christianity in the middle ages it has become perverted by some people in order to further their political ends.

Medieval intolerance with modern weapons. As alien as they seem to us, Al Qaeda would have been instantly recognized by Torquemada, and perhaps respected as an enemy worthy of his own holy war.