Your point would make sense if it wasnt for the fact that it seems 90% of ISIS militants are from North Africa, Saudi, etc etc who have had little direct impact apart from the fact that "fellow muslims" suffered, yet ironically will blow up a marketplace and kill a hundred of their "fellow muslims" without thinking twice.
The direct cause is the Iraq war but the bad people were always there, Saddam just oppressed them but towards the end of his reign there was alot of extremists (Fedayeen? not sure) grouping in the country. The war may have started it but this was an inevitable problem, how were the terrorists who are wealthy people from gulf states suffer from the Iraq war? There are far too many young men in Muslim/non Muslim countries who feel like they dont belong, the real cause of todays problem isnt the Iraq war, its the modern connectivity of humanity and people can feel out of place very quickly and look for alternatives because doing something resulting in death is often an easier way out than struggling with a life of poverty/mediocrity for decades, I know it would appeal to my mindset if I lived in a country like Algeria, work for peanuts slaving away all your life or go on an adventure firing guns and feeling brotherhood, its a great alternative to life in many modern Islamic countries and one that I can completely understand given the opportunities in many of these countries. All young men have a inbuilt desire to fight, its just most have too good of a life to give up.