An 18th century preacher was born in what is Najd, Saudi Arabia -- Muhammed ibn Abd al-Wahhab. To understand Saudi Arabia (and ISIS for that matter) is to understand him. He started the Wahabbi movement which is an orthodox, right wing & frankly off the wall sect of Sunni Islam.
http://en.wikipedia.org/wiki/Muhammad_ibn_Abd_al-Wahhab
He formed a pact with Muhammad bin Saud who was a devoted follower
"You are the settlement's chief and wise man. I want you to grant me an oath that you will perform jihad (Struggle to spread Islam) against the unbelievers. In return you will be imam, leader of the Muslim community and I will be leader in religious matters."
He started a bloody campaign that spilled a lot of blood & beheadings to establish The First Saudi State which led to the Saudi Dynasty eventually led to Saudi Arabia in the early 1900s which led to the 'House of Saud' and eventually other Wahabbi kingdoms such as Kuwait, UAB, Qatar, and maybe others.
California Oil Company (later Chevron) found oil in Saudi Arabia in the 1930s which was turning point for the Wahabbi movement because of its partnership with the United States
http://fpif.org/us_oil_policy_in_the_middle_east/
In the 1950s and 60s within Saudi Arabia, the Wahhabi ulama maintained their hold on religious law courts, presided over the creation of Islamic universities, and a public school system which gave students "a heavy dose of religious instruction".[151] Outside of Saudi the Wahhabi ulama became "less combative" toward the rest of the Muslim world. In confronting the challenge of the West, Wahhabi doctrine "served well" for many Muslims as a "platform" and "gained converts beyond the peninsula."[151][152]
Here is a good documentary
Also you can read about CIA, Reagan, Osama bin laden, and Saudi Arabia to learn about Al-Qaeda who are Wahabbi which explains why the Saudi Arabia funded them & their mutual dislike of communism to explain why the US was involved to fight a proxy war against the USSR.
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