From the devastating war in Syria, to the crisis in Yemen, to continuing turmoil in Iraq, much of today's widespread violence across the Middle East has been portrayed as part of an ancient battle between the Sunni and Shia branches of Islam. 

In Bitter Rivals: Iran and Saudi Arabia, FRONTLINE tells the epic, inside story of how this dangerous feud has plunged the Middle East into unprecedented levels of violence - with exclusive, on-the-ground reporting from inside both countries as well as Yemen, Iraq, Pakistan, Syria, and Lebanon. 

Bitter Rivals illuminates the essential history - and profound ripple effect - of Iran and Saudi Arabia's power struggle. It draws on scores of interviews with political, religious and military leaders, militia commanders, diplomats, and policy experts, painting American television's most comprehensive picture of a feud that has reshaped the Middle East.