Not at all justifiying any acts of terror, just want to give my perspective on this. We, allied nations, and mostly US have had boots, in massive numbers, on middle east ground for over 20 years. This not only helps getting rid of current threats but also breeds confusion, hatred and new branches of extremist groups like ISIS. Someone said before Bush Sr's invasion of Iraq in the 90's, that it was going to be the same as kicking a hornets nest, and that attacks on western countries should be expected. Stuff has been real for decades.