Well, this would seem to be the issue/question of the century! The answer, just keep the bastards out! You can't tell by looking and it only stands to reason that just like everywhere, including still in Iraq today, that once a large base of muslims exists, then you have these issues. How can you stop it? You can't apart from altering behavior which has been born out that it can't be altered!
The roots, two religions, or one really, Judeo-Christianity with its roots in "love everyone", all the way down to your neighbor, vs. Islam, with its roots in take over the world and force, necessarily in one form or another, everyone to either convert or acquiesse to Islam, or kill them quite simply.
Too bad more Canadians and Englanders don't think this way!
All over the world where slaughter and human rights violence is peaking, somewhere in there, usually from the top in one way or another, it's Islam that is leading the charge!
Meanwhile, where Judeo/Christian based nations are the order of the day, it's by and large extremely peaceful and civilized.
But hey, as long as people "seek to understand" instead of simply dealing with truth, this crap is gonna spread. It wouldn't hurt the "non-militant" version of Islam to stand up and be counted on the side of the good guys however. And there's FAR too little of that going on!
In fact, it's rare if even occurrent at all, for Islamic nations to "be outraged" to the extent of action in all of this. I'm convinced this is why it's a slow train coming in Iraq with the political changeover and the transition of the Iraqis to begin to learn to defend themselves as well.