There seems to be a reason for this 'sudden' increase in Islamic terror throughout the West.
We hardly saw any of it, aside from that associated with the Palestinian issue, prior to the start of the century. On top of which much of it seems to be increasingly fomented by nationals and in many cases by converts to Islam. My theory is that collapse of the Christian social and cultural character of the West has left a vacuum into which Islam is surging.
Like it or not young people, and especially young men, have an innate need for a rigorous, morally explicit, critically defined faith which put onerous demands of proof upon them. They need a CODE and a stable conception of the universe. That is something that secular humanism, with all of its relativism, materialism and nihilism, which forms the basis post modern belief system of the West can never provide. That will always implicity agnostic, if not outrightly atheistic.. and founded in a profound pessimism and doubt.
So the West has really brought this on itself when it decided that, in all constitutional definitions, it is beyond superstitions such as belief in God.. and especially in Christ. As morally deformed as Islam is, it still represents something substantially certain, with which the West can no longer compete. And its only going to get worse.