Saudi and Iran hatred goes back long before that. Shia vs Sunni. Genesis of most of the problems in middle east. Syrian civil war: Sunni vs Alawites(Shia offshoot). Yemen civil war: Sunni vs Shia. When a mosque is bombed somewhere in middle east, its sunni vs Shia. It makes for some interesting decisions on support from the US side. We are now backing the new president of Syria who spent had spent a decade killing Americans in Iraq when he was leadership in Iraqi Al Qaeda.