Root cause:  "For 5 decades, Saudi Arabia has spread its narrow, puritanical and intolerant version of Islam, originally practiced almost nowhere else, across the Muslim world.... Saudi money is now transforming European Islam.  Leaked German intelligence reports now show that charities closely connected with government offices of Saudi Arabia, Qatar and Kuwait are funding mosques, schools and Imams to disseminate a fundamentalist intolerant version of Islam throughout Germany..." Fareed Zakaria

http://www.cnn.com/videos/politics/2017/05/28/fareeds-take-saudi-arabia-terrorism.cnn

This is not new.  Middle East scholars wrote books about this BEFORE 9/11.  And Trump who once espoused these ideas now targets (Shiite) Iran.  Unbelievable (as it was when Bush targeted Iraq). Money changes everything.