The Big Split in the Revolutionary Islamist Movement: Sunni and Shia Blocs Emerge

"A development of huge importance is happening in the Middle East, equivalent perhaps to the Sino-Soviet conflict’s effect on the Cold War era: the division of revolutionary Islamists into separate Sunni and Shia camps.

Of course, there have always been tensions and conflicts between Sunni and Shia Muslims, notably bloody fighting in Iraq. Islamists often attempt to portray this as a Western conspiracy but most Muslims know it is a historical reality within Islam."
The Rubin Report