From what I can tell it goes like this: The majority of terrorists in the 9/11 attacks were Saudi Arabian, Osama Bin Laden of course was from a wealthy Saudi family with ties to the ruling Royalty and it is alleged that there was some assistance from some elements within the Saudi government in 9/11 – see 28pages.org for more on this.
Because of this terrorist attack, Iraq was invaded, leading to the formation of ISIS. Saudi individuals have been responsible for funding ISIS. But Saudi Arabia is officially allied with ‘The West’ against them, in spite of spending billions and billions in promoting its hard line Wahhabist interpretation of Islam which is said to be integral in the spread of extremism.
Everything clear? Good.