They believed in the wrong God my freind the God Muslims beleive in and the God as in the trinity God the father son and Holy Ghost are 2 different things also there are people that are warped that htink blowing up an abortion clinic is the right way to do things. I fully disagree with all of that please do not assume and put everyone in the same catagory. the warning is that the towers are a sensative subject as I have lost freinds of my own soilders too.
Actually what the Al-Qaeda members did was response the call of the
jihad, and the jihad(or holy war) is only invoked when one the Muslim believes there is a thread to their society or their community(defence of the Muslim), under these bases a more accurate representation of this is a call to war to protect their people, not by following the wrong god but by following the Muslim doctrine(which Al-Qaeda used as excuse to get militants into their terrorist attacks, and execute their attacks with suicide bombers).
For the sake of reference and before I get mistakenly identified as Muslim I should add that I don't believe in any kind of god or supreme being, because such thing is a creation of the human psyche to fulfils a need of support and reliability(me thinks, and by IRL experience this has been proven right thus far).
Now regarding the whole Islam god/Christian god there are two things that should be acknowledged, for one we can find that Jesus is identify by the Muslim as one of the prophets from Allah(as Isa to be precise), and the second would be the
Constitution of Medina which basically worked as a union of the different beliefs to create a single nation written in the Quran(which is the Muslim equivalent of the bible) and can be consider as today's common believe of a western God.
Just like the Bible, the Quran was constantly updated and is some cases reformed as time changed, just like the Bible most of its original doctrines and rules set by the original prophet(in this case Muhammad) were changed or modified(in the case of the Quran this should not happen).
Now if both cases are explored is not hard to identify the existing similitude between both books(apart from being records and doctrine guides), but one thing that takes my attention in the Quran is the emphasis(not complete but constantly mentioned)on the knowledge as a fundamental base for this doctrine(and one of the main proprieties of their own god).
With this my point is this, the "doctrine" and its evolution depend only on the region in which these are evolved, a more actual(but absolute) representation of a god would be the one given by the Taoists in chine by consider nature and balance as the main elements that replaces the concept of all powerful god.
Here we find these 3 aspects of global religious beliefs which doesn't coherent which other and only demonstrates that the general idea of a single god(or the mere definition of it) doesn't actually exist, and only exists as an idea rather than a fact.
For quick reference consider the number believers in their respective doctrine(or religion):
>Taoists(200-400 million)
>Muslim(1.3-1.57 billion, around 21-23% of world's population)
>Christians(2.2 billion, around +25 of world's population)
Unfortunately these numbers are rounded based on very vague information, but is not as inaccurate to consider my point of population ratio/believe as incorrect.
And unfortunately I didn't consider Buddhists for this comparison(which is also a significant number in relation to the global population).