Adam Curtis just came out with an incredible documentary titled 'Bitter Lake' which details the origins of the United State's relationship with Saudi Arabia and how the terms of that relationship have impacted the development of terrorism in the Middle East, especially Afghanistan.

It's an intrinsically relevant part of this conversation (especially considering Saudi Arabia's adherence to and history of practicing wahhabism) and I'd encourage others to check it out: https://www.youtube.com/watch?v=jXcpDO8_3qU