There's always been violent sects, but Islamic terrorism in it's current form is a very modern phenomenon. The modern founders of this ideology were originally non-violent anti-liberals who popped up in the 50's, but we tortured the hate into them. We then created the entire concept of the "foreign fighter" and the modern jihad when we recruited stupid young men to fight a proxy war against the soviets for us. Coincidentally(?), it's only after this campaign of funded Islamism that this list begins. Also coincidentally(?), the list explodes after the "war on terror".
That's not to mention that we literally illegally destroyed the nations or Iraq and Libya and converted them into hotbeds of terrorism. In the latter case we actually directly funded the Islamist and handed them the failed state on a silver platter, just like 1980's Afghanistan all over again... Meanwhile we were funding Islamists in Syria and supplying / training them, as were and are our allies, Turkey and Saudi Arabia.
To me, it seems ass-backwards to wring our hands after events like this and wonder what we should be doing to fix the problem, when we are literally creating the problem.
Stop voting for invaders and paying taxes to their armies. I'm sorry, but wars of aggression are wrong. It's pretty damn simple.
The US army originally wasn't supposed to exist, and then was only supposed to be used defensively following a declaration of war. The last time that happened was WW2. Since then, they've illegally invaded Korea, Lebanon, Cuba, the Congo, Domincan Republic, Vietnam, Thailand, Grenada, Iran, Republic of Panama, Iraq, Somalia, Haiti, Bosnia and Herzegovina/Serbia/Yugoslavia, Afghanistan, Pakistan, Libya, Syria without ever producing a declaration of war. And that's the official list. There's economic, political, proxy and black acts of war also carried out with plausible deniability against almost every other country in the world. There's countless democracies overthrown by CIA-backed coups, and propped up dictators. This is not freedom; this is a rogue state...
Bush Jr. started the current US war against Syria - it goes back that far! It wasn't a real declared war of course -- Bush only got congress to approve a proxy war by funding anti-government forces there - i.e. stirring up civil war... Obama continued those programs, actually invaded it with the US military, and conspired to destroy Libya beforehand too, by funding the terrorist rebellion there, along with a secret Egyptian ground invasion and air support from NATO countries.
Start respecting sovereignty, stop destroying parts of civilization, and the barbarians will stop appearing in those voids.
Don't obsess over the symptoms, address the actual illness: war.